diff --git a/Plugins/BridgeJS/Package.swift b/Plugins/BridgeJS/Package.swift
index 01a3c6d4..a03172f1 100644
--- a/Plugins/BridgeJS/Package.swift
+++ b/Plugins/BridgeJS/Package.swift
@@ -72,7 +72,7 @@ let package = Package(
             name: "BridgeJSMacrosTests",
             dependencies: [
                 "BridgeJSMacros",
-                .product(name: "SwiftSyntaxMacrosTestSupport", package: "swift-syntax"),
+                .product(name: "SwiftSyntaxMacrosGenericTestSupport", package: "swift-syntax"),
             ]
         ),
 
diff --git a/Plugins/BridgeJS/Sources/BridgeJSMacros/JSClassMacro.swift b/Plugins/BridgeJS/Sources/BridgeJSMacros/JSClassMacro.swift
index 8a3f83f0..2641df4b 100644
--- a/Plugins/BridgeJS/Sources/BridgeJSMacros/JSClassMacro.swift
+++ b/Plugins/BridgeJS/Sources/BridgeJSMacros/JSClassMacro.swift
@@ -66,9 +66,16 @@ extension JSClassMacro: ExtensionMacro {
         conformingTo protocols: [TypeSyntax],
         in context: some MacroExpansionContext
     ) throws -> [ExtensionDeclSyntax] {
-        guard declaration.is(StructDeclSyntax.self) else { return [] }
+        guard let structDecl = declaration.as(StructDeclSyntax.self) else { return [] }
         guard !protocols.isEmpty else { return [] }
 
+        // Do not add extension if the struct already conforms to _JSBridgedClass
+        if let clause = structDecl.inheritanceClause,
+            clause.inheritedTypes.contains(where: { $0.type.trimmed.description == "_JSBridgedClass" })
+        {
+            return []
+        }
+
         let conformanceList = protocols.map { $0.trimmed.description }.joined(separator: ", ")
         return [
             try ExtensionDeclSyntax("extension \(type.trimmed): \(raw: conformanceList) {}")
diff --git a/Plugins/BridgeJS/Sources/BridgeJSMacros/JSFunctionMacro.swift b/Plugins/BridgeJS/Sources/BridgeJSMacros/JSFunctionMacro.swift
index 7dfd635f..a51bf10c 100644
--- a/Plugins/BridgeJS/Sources/BridgeJSMacros/JSFunctionMacro.swift
+++ b/Plugins/BridgeJS/Sources/BridgeJSMacros/JSFunctionMacro.swift
@@ -47,7 +47,7 @@ extension JSFunctionMacro: BodyMacro {
                 context.diagnose(
                     Diagnostic(node: Syntax(declaration), message: JSMacroMessage.unsupportedDeclaration)
                 )
-                return []
+                return [CodeBlockItemSyntax(stringLiteral: "fatalError(\"@JSFunction init must be inside a type\")")]
             }
 
             let glueName = JSMacroHelper.glueName(baseName: "init", enclosingTypeName: enclosingTypeName)
@@ -70,3 +70,19 @@ extension JSFunctionMacro: BodyMacro {
         return []
     }
 }
+
+extension JSFunctionMacro: PeerMacro {
+    /// Emits a diagnostic when @JSFunction is applied to a declaration that is not a function or initializer.
+    /// BodyMacro is only invoked for declarations with optional code blocks (e.g. functions, initializers),
+    /// so for vars and other decls we need PeerMacro to run and diagnose.
+    public static func expansion(
+        of node: AttributeSyntax,
+        providingPeersOf declaration: some DeclSyntaxProtocol,
+        in context: some MacroExpansionContext
+    ) throws -> [DeclSyntax] {
+        if declaration.is(FunctionDeclSyntax.self) { return [] }
+        if declaration.is(InitializerDeclSyntax.self) { return [] }
+        context.diagnose(Diagnostic(node: Syntax(declaration), message: JSMacroMessage.unsupportedDeclaration))
+        return []
+    }
+}
diff --git a/Plugins/BridgeJS/Sources/BridgeJSMacros/JSGetterMacro.swift b/Plugins/BridgeJS/Sources/BridgeJSMacros/JSGetterMacro.swift
index b996facf..44c3620c 100644
--- a/Plugins/BridgeJS/Sources/BridgeJSMacros/JSGetterMacro.swift
+++ b/Plugins/BridgeJS/Sources/BridgeJSMacros/JSGetterMacro.swift
@@ -60,3 +60,20 @@ extension JSGetterMacro: AccessorMacro {
         ]
     }
 }
+
+extension JSGetterMacro: PeerMacro {
+    /// Emits a diagnostic when @JSGetter is applied to a declaration that is not a variable (e.g. a function).
+    /// AccessorMacro may not be invoked for non-property declarations. For variables with multiple
+    /// bindings, the compiler emits its own diagnostic; we only diagnose non-variable decls here.
+    public static func expansion(
+        of node: AttributeSyntax,
+        providingPeersOf declaration: some DeclSyntaxProtocol,
+        in context: some MacroExpansionContext
+    ) throws -> [DeclSyntax] {
+        guard declaration.is(VariableDeclSyntax.self) else {
+            context.diagnose(Diagnostic(node: Syntax(declaration), message: JSMacroMessage.unsupportedVariable))
+            return []
+        }
+        return []
+    }
+}
diff --git a/Plugins/BridgeJS/Sources/BridgeJSMacros/JSSetterMacro.swift b/Plugins/BridgeJS/Sources/BridgeJSMacros/JSSetterMacro.swift
index bb9fd1f2..3c728007 100644
--- a/Plugins/BridgeJS/Sources/BridgeJSMacros/JSSetterMacro.swift
+++ b/Plugins/BridgeJS/Sources/BridgeJSMacros/JSSetterMacro.swift
@@ -25,13 +25,23 @@ extension JSSetterMacro: BodyMacro {
         let rawFunctionName = JSMacroHelper.stripBackticks(functionName)
         guard rawFunctionName.hasPrefix("set"), rawFunctionName.count > 3 else {
             context.diagnose(Diagnostic(node: Syntax(declaration), message: JSMacroMessage.invalidSetterName))
-            return []
+            return [
+                CodeBlockItemSyntax(
+                    stringLiteral:
+                        "fatalError(\"@JSSetter function name must start with 'set' followed by a property name\")"
+                )
+            ]
         }
 
         let propertyName = String(rawFunctionName.dropFirst(3))
         guard !propertyName.isEmpty else {
             context.diagnose(Diagnostic(node: Syntax(declaration), message: JSMacroMessage.invalidSetterName))
-            return []
+            return [
+                CodeBlockItemSyntax(
+                    stringLiteral:
+                        "fatalError(\"@JSSetter function name must start with 'set' followed by a property name\")"
+                )
+            ]
         }
 
         // Convert first character to lowercase (e.g., "Foo" -> "foo")
@@ -56,7 +66,11 @@ extension JSSetterMacro: BodyMacro {
         let parameters = functionDecl.signature.parameterClause.parameters
         guard let firstParam = parameters.first else {
             context.diagnose(Diagnostic(node: Syntax(declaration), message: JSMacroMessage.setterRequiresParameter))
-            return []
+            return [
+                CodeBlockItemSyntax(
+                    stringLiteral: "fatalError(\"@JSSetter function must have at least one parameter\")"
+                )
+            ]
         }
 
         let paramName = firstParam.secondName ?? firstParam.firstName
@@ -69,3 +83,21 @@ extension JSSetterMacro: BodyMacro {
         return [CodeBlockItemSyntax(stringLiteral: "try \(call)")]
     }
 }
+
+extension JSSetterMacro: PeerMacro {
+    /// Emits a diagnostic when @JSSetter is applied to a declaration that is not a function.
+    /// BodyMacro is only invoked for declarations with optional code blocks (e.g. functions).
+    public static func expansion(
+        of node: AttributeSyntax,
+        providingPeersOf declaration: some DeclSyntaxProtocol,
+        in context: some MacroExpansionContext
+    ) throws -> [DeclSyntax] {
+        guard declaration.is(FunctionDeclSyntax.self) else {
+            context.diagnose(
+                Diagnostic(node: Syntax(declaration), message: JSMacroMessage.unsupportedSetterDeclaration)
+            )
+            return []
+        }
+        return []
+    }
+}
diff --git a/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSClassMacroTests.swift b/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSClassMacroTests.swift
index b27b9394..7640916e 100644
--- a/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSClassMacroTests.swift
+++ b/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSClassMacroTests.swift
@@ -1,8 +1,7 @@
 import SwiftDiagnostics
 import SwiftSyntax
 import SwiftSyntaxMacroExpansion
-import SwiftSyntaxMacros
-import SwiftSyntaxMacrosTestSupport
+import SwiftSyntaxMacrosGenericTestSupport
 import Testing
 import BridgeJSMacros
 
@@ -13,7 +12,7 @@ import BridgeJSMacros
     ]
 
     @Test func emptyStruct() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSClass
             struct MyClass {
@@ -21,6 +20,7 @@ import BridgeJSMacros
             """,
             expandedSource: """
                 struct MyClass {
+
                     let jsObject: JSObject
 
                     init(unsafelyWrapping jsObject: JSObject) {
@@ -32,12 +32,12 @@ import BridgeJSMacros
                 }
                 """,
             macroSpecs: macroSpecs,
-            indentationWidth: indentationWidth
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func structWithExistingJSObject() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSClass
             struct MyClass {
@@ -62,7 +62,7 @@ import BridgeJSMacros
     }
 
     @Test func structWithExistingInit() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSClass
             struct MyClass {
@@ -73,11 +73,11 @@ import BridgeJSMacros
             """,
             expandedSource: """
                 struct MyClass {
-                    let jsObject: JSObject
-
                     init(unsafelyWrapping jsObject: JSObject) {
                         self.jsObject = jsObject
                     }
+
+                    let jsObject: JSObject
                 }
 
                 extension MyClass: _JSBridgedClass {
@@ -89,7 +89,7 @@ import BridgeJSMacros
     }
 
     @Test func structWithBothExisting() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSClass
             struct MyClass {
@@ -118,7 +118,7 @@ import BridgeJSMacros
     }
 
     @Test func structWithMembers() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSClass
             struct MyClass {
@@ -127,10 +127,10 @@ import BridgeJSMacros
             """,
             expandedSource: """
                 struct MyClass {
-                    let jsObject: JSObject
-
                     var name: String
 
+                    let jsObject: JSObject
+
                     init(unsafelyWrapping jsObject: JSObject) {
                         self.jsObject = jsObject
                     }
@@ -145,7 +145,7 @@ import BridgeJSMacros
     }
 
     @Test func _class() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSClass
             class MyClass {
@@ -168,7 +168,7 @@ import BridgeJSMacros
     }
 
     @Test func _enum() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSClass
             enum MyEnum {
@@ -191,7 +191,7 @@ import BridgeJSMacros
     }
 
     @Test func _actor() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSClass
             actor MyActor {
@@ -214,7 +214,7 @@ import BridgeJSMacros
     }
 
     @Test func structWithDifferentJSObjectName() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSClass
             struct MyClass {
@@ -223,10 +223,10 @@ import BridgeJSMacros
             """,
             expandedSource: """
                 struct MyClass {
-                    let jsObject: JSObject
-
                     var otherProperty: String
 
+                    let jsObject: JSObject
+
                     init(unsafelyWrapping jsObject: JSObject) {
                         self.jsObject = jsObject
                     }
@@ -241,7 +241,7 @@ import BridgeJSMacros
     }
 
     @Test func structWithDifferentInit() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSClass
             struct MyClass {
@@ -251,11 +251,11 @@ import BridgeJSMacros
             """,
             expandedSource: """
                 struct MyClass {
-                    let jsObject: JSObject
-
                     init(name: String) {
                     }
 
+                    let jsObject: JSObject
+
                     init(unsafelyWrapping jsObject: JSObject) {
                         self.jsObject = jsObject
                     }
@@ -270,7 +270,7 @@ import BridgeJSMacros
     }
 
     @Test func structWithMultipleMembers() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSClass
             struct MyClass {
@@ -280,11 +280,11 @@ import BridgeJSMacros
             """,
             expandedSource: """
                 struct MyClass {
-                    let jsObject: JSObject
-
                     var name: String
                     var age: Int
 
+                    let jsObject: JSObject
+
                     init(unsafelyWrapping jsObject: JSObject) {
                         self.jsObject = jsObject
                     }
@@ -299,7 +299,7 @@ import BridgeJSMacros
     }
 
     @Test func structWithComment() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             /// Documentation comment
             @JSClass
@@ -309,6 +309,7 @@ import BridgeJSMacros
             expandedSource: """
                 /// Documentation comment
                 struct MyClass {
+
                     let jsObject: JSObject
 
                     init(unsafelyWrapping jsObject: JSObject) {
@@ -325,7 +326,7 @@ import BridgeJSMacros
     }
 
     @Test func structAlreadyConforms() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSClass
             struct MyClass: _JSBridgedClass {
@@ -333,6 +334,7 @@ import BridgeJSMacros
             """,
             expandedSource: """
                 struct MyClass: _JSBridgedClass {
+
                     let jsObject: JSObject
 
                     init(unsafelyWrapping jsObject: JSObject) {
diff --git a/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSFunctionMacroTests.swift b/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSFunctionMacroTests.swift
index 8cfdd66e..756935e7 100644
--- a/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSFunctionMacroTests.swift
+++ b/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSFunctionMacroTests.swift
@@ -1,15 +1,18 @@
 import SwiftDiagnostics
 import SwiftSyntax
-import SwiftSyntaxMacros
-import SwiftSyntaxMacrosTestSupport
+import SwiftSyntaxMacroExpansion
+import SwiftSyntaxMacrosGenericTestSupport
 import Testing
 import BridgeJSMacros
 
 @Suite struct JSFunctionMacroTests {
     private let indentationWidth: Trivia = .spaces(4)
+    private let macroSpecs: [String: MacroSpec] = [
+        "JSFunction": MacroSpec(type: JSFunctionMacro.self)
+    ]
 
     @Test func topLevelFunction() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSFunction
             func greet(name: String) -> String
@@ -19,13 +22,13 @@ import BridgeJSMacros
                     return _$greet(name)
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func topLevelFunctionVoidReturn() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSFunction
             func log(message: String)
@@ -35,13 +38,13 @@ import BridgeJSMacros
                     _$log(message)
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func topLevelFunctionWithExplicitVoidReturn() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSFunction
             func log(message: String) -> Void
@@ -51,13 +54,13 @@ import BridgeJSMacros
                     _$log(message)
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func topLevelFunctionWithEmptyTupleReturn() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSFunction
             func log(message: String) -> ()
@@ -67,13 +70,13 @@ import BridgeJSMacros
                     _$log(message)
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func topLevelFunctionThrows() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSFunction
             func parse(json: String) throws -> [String: Any]
@@ -83,13 +86,13 @@ import BridgeJSMacros
                     return try _$parse(json)
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func topLevelFunctionAsync() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSFunction
             func fetch(url: String) async -> String
@@ -99,13 +102,13 @@ import BridgeJSMacros
                     return await _$fetch(url)
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func topLevelFunctionAsyncThrows() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSFunction
             func fetch(url: String) async throws -> String
@@ -115,13 +118,13 @@ import BridgeJSMacros
                     return try await _$fetch(url)
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func topLevelFunctionWithUnderscoreParameter() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSFunction
             func process(_ value: Int) -> Int
@@ -131,13 +134,13 @@ import BridgeJSMacros
                     return _$process(value)
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func topLevelFunctionWithMultipleParameters() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSFunction
             func add(a: Int, b: Int) -> Int
@@ -147,13 +150,13 @@ import BridgeJSMacros
                     return _$add(a, b)
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func instanceMethod() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             struct MyClass {
                 @JSFunction
@@ -167,13 +170,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func staticMethod() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             struct MyClass {
                 @JSFunction
@@ -183,17 +186,17 @@ import BridgeJSMacros
             expandedSource: """
                 struct MyClass {
                     static func create() -> MyClass {
-                        return _$create()
+                        return _$MyClass_create()
                     }
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func classMethod() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             class MyClass {
                 @JSFunction
@@ -203,17 +206,17 @@ import BridgeJSMacros
             expandedSource: """
                 class MyClass {
                     class func create() -> MyClass {
-                        return _$create()
+                        return _$MyClass_create()
                     }
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func initializer() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             struct MyClass {
                 @JSFunction
@@ -228,13 +231,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func initializerThrows() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             struct MyClass {
                 @JSFunction
@@ -249,13 +252,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func initializerAsyncThrows() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             struct MyClass {
                 @JSFunction
@@ -270,19 +273,21 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func initializerWithoutEnclosingType() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSFunction
             init()
             """,
             expandedSource: """
-                init()
+                init() {
+                    fatalError("@JSFunction init must be inside a type")
+                }
                 """,
             diagnostics: [
                 DiagnosticSpec(
@@ -291,13 +296,13 @@ import BridgeJSMacros
                     column: 1
                 )
             ],
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func unsupportedDeclaration() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSFunction
             var property: String
@@ -312,13 +317,13 @@ import BridgeJSMacros
                     column: 1
                 )
             ],
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func enumInstanceMethod() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             enum MyEnum {
                 @JSFunction
@@ -332,13 +337,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func actorInstanceMethod() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             actor MyActor {
                 @JSFunction
@@ -352,13 +357,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func functionWithExistingBody() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSFunction
             func greet(name: String) -> String {
@@ -370,8 +375,8 @@ import BridgeJSMacros
                     return _$greet(name)
                 }
                 """,
-            macros: ["JSFunction": JSFunctionMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 }
diff --git a/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSGetterMacroTests.swift b/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSGetterMacroTests.swift
index 8c7f3c11..2796c101 100644
--- a/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSGetterMacroTests.swift
+++ b/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSGetterMacroTests.swift
@@ -1,15 +1,18 @@
 import SwiftDiagnostics
 import SwiftSyntax
-import SwiftSyntaxMacros
-import SwiftSyntaxMacrosTestSupport
+import SwiftSyntaxMacroExpansion
+import SwiftSyntaxMacrosGenericTestSupport
 import Testing
 import BridgeJSMacros
 
 @Suite struct JSGetterMacroTests {
     private let indentationWidth: Trivia = .spaces(4)
+    private let macroSpecs: [String: MacroSpec] = [
+        "JSGetter": MacroSpec(type: JSGetterMacro.self)
+    ]
 
     @Test func topLevelVariable() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSGetter
             var count: Int
@@ -21,13 +24,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func topLevelLet() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSGetter
             let constant: String
@@ -39,13 +42,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func instanceProperty() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             struct MyClass {
                 @JSGetter
@@ -61,13 +64,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func instanceLetProperty() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             struct MyClass {
                 @JSGetter
@@ -83,13 +86,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func staticProperty() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             struct MyClass {
                 @JSGetter
@@ -100,18 +103,18 @@ import BridgeJSMacros
                 struct MyClass {
                     static var version: String {
                         get throws(JSException) {
-                            return try _$version_get()
+                            return try _$MyClass_version_get()
                         }
                     }
                 }
                 """,
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func classProperty() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             class MyClass {
                 @JSGetter
@@ -122,18 +125,18 @@ import BridgeJSMacros
                 class MyClass {
                     class var version: String {
                         get throws(JSException) {
-                            return try _$version_get()
+                            return try _$MyClass_version_get()
                         }
                     }
                 }
                 """,
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func enumProperty() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             enum MyEnum {
                 @JSGetter
@@ -149,13 +152,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func actorProperty() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             actor MyActor {
                 @JSGetter
@@ -171,13 +174,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func variableWithExistingAccessor() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSGetter
             var count: Int {
@@ -194,13 +197,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func variableWithInitializer() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSGetter
             var count: Int = 0
@@ -212,13 +215,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func multipleBindings() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSGetter
             var x: Int, y: Int
@@ -228,19 +231,25 @@ import BridgeJSMacros
                 """,
             diagnostics: [
                 DiagnosticSpec(
-                    message: "@JSGetter can only be applied to single-variable declarations.",
+                    message: "accessor macro can only be applied to a single variable",
                     line: 1,
                     column: 1,
                     severity: .error
-                )
+                ),
+                DiagnosticSpec(
+                    message: "peer macro can only be applied to a single variable",
+                    line: 1,
+                    column: 1,
+                    severity: .error
+                ),
             ],
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func unsupportedDeclaration() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSGetter
             func test() {}
@@ -256,13 +265,15 @@ import BridgeJSMacros
                     severity: .error
                 )
             ],
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
+    #if canImport(SwiftSyntax601)
+    // https://github.com/swiftlang/swift-syntax/pull/2722
     @Test func variableWithTrailingComment() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSGetter
             var count: Int // comment
@@ -274,13 +285,14 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
+    #endif
 
     @Test func variableWithUnderscoreName() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSGetter
             var _internal: String
@@ -288,12 +300,12 @@ import BridgeJSMacros
             expandedSource: """
                 var _internal: String {
                     get throws(JSException) {
-                        return try _$internal_get()
+                        return try _$_internal_get()
                     }
                 }
                 """,
-            macros: ["JSGetter": JSGetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 }
diff --git a/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSSetterMacroTests.swift b/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSSetterMacroTests.swift
index 83289e09..1ed4e108 100644
--- a/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSSetterMacroTests.swift
+++ b/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/JSSetterMacroTests.swift
@@ -1,15 +1,18 @@
 import SwiftDiagnostics
 import SwiftSyntax
-import SwiftSyntaxMacros
-import SwiftSyntaxMacrosTestSupport
+import SwiftSyntaxMacroExpansion
+import SwiftSyntaxMacrosGenericTestSupport
 import Testing
 import BridgeJSMacros
 
 @Suite struct JSSetterMacroTests {
     private let indentationWidth: Trivia = .spaces(4)
+    private let macroSpecs: [String: MacroSpec] = [
+        "JSSetter": MacroSpec(type: JSSetterMacro.self)
+    ]
 
     @Test func topLevelSetter() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSSetter
             func setFoo(_ value: Foo) throws(JSException)
@@ -19,13 +22,13 @@ import BridgeJSMacros
                     try _$foo_set(value)
                 }
                 """,
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func topLevelSetterWithNamedParameter() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSSetter
             func setCount(count: Int) throws(JSException)
@@ -35,13 +38,13 @@ import BridgeJSMacros
                     try _$count_set(count)
                 }
                 """,
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func instanceSetter() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             struct MyClass {
                 @JSSetter
@@ -55,13 +58,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func staticSetter() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             struct MyClass {
                 @JSSetter
@@ -71,17 +74,17 @@ import BridgeJSMacros
             expandedSource: """
                 struct MyClass {
                     static func setVersion(_ version: String) throws(JSException) {
-                        try _$version_set(version)
+                        try _$MyClass_version_set(version)
                     }
                 }
                 """,
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func classSetter() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             class MyClass {
                 @JSSetter
@@ -91,17 +94,17 @@ import BridgeJSMacros
             expandedSource: """
                 class MyClass {
                     class func setConfig(_ config: Config) throws(JSException) {
-                        try _$config_set(config)
+                        try _$MyClass_config_set(config)
                     }
                 }
                 """,
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func enumSetter() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             enum MyEnum {
                 @JSSetter
@@ -115,13 +118,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func actorSetter() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             actor MyActor {
                 @JSSetter
@@ -135,13 +138,13 @@ import BridgeJSMacros
                     }
                 }
                 """,
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func setterWithExistingBody() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSSetter
             func setFoo(_ value: Foo) throws(JSException) {
@@ -153,19 +156,21 @@ import BridgeJSMacros
                     try _$foo_set(value)
                 }
                 """,
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func invalidSetterName() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSSetter
             func updateFoo(_ value: Foo) throws(JSException)
             """,
             expandedSource: """
-                func updateFoo(_ value: Foo) throws(JSException)
+                func updateFoo(_ value: Foo) throws(JSException) {
+                    fatalError("@JSSetter function name must start with 'set' followed by a property name")
+                }
                 """,
             diagnostics: [
                 DiagnosticSpec(
@@ -175,19 +180,21 @@ import BridgeJSMacros
                     column: 1
                 )
             ],
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func setterNameTooShort() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSSetter
             func set(_ value: Foo) throws(JSException)
             """,
             expandedSource: """
-                func set(_ value: Foo) throws(JSException)
+                func set(_ value: Foo) throws(JSException) {
+                    fatalError("@JSSetter function name must start with 'set' followed by a property name")
+                }
                 """,
             diagnostics: [
                 DiagnosticSpec(
@@ -197,19 +204,21 @@ import BridgeJSMacros
                     column: 1
                 )
             ],
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func setterWithoutParameter() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSSetter
             func setFoo() throws(JSException)
             """,
             expandedSource: """
-                func setFoo() throws(JSException)
+                func setFoo() throws(JSException) {
+                    fatalError("@JSSetter function must have at least one parameter")
+                }
                 """,
             diagnostics: [
                 DiagnosticSpec(
@@ -218,13 +227,13 @@ import BridgeJSMacros
                     column: 1
                 )
             ],
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func unsupportedDeclaration() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSSetter
             var property: String
@@ -239,13 +248,13 @@ import BridgeJSMacros
                     column: 1
                 )
             ],
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func setterWithMultipleWords() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSSetter
             func setConnectionTimeout(_ timeout: Int) throws(JSException)
@@ -255,13 +264,13 @@ import BridgeJSMacros
                     try _$connectionTimeout_set(timeout)
                 }
                 """,
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 
     @Test func setterWithSingleLetterProperty() {
-        assertMacroExpansion(
+        TestSupport.assertMacroExpansion(
             """
             @JSSetter
             func setX(_ x: Int) throws(JSException)
@@ -271,8 +280,8 @@ import BridgeJSMacros
                     try _$x_set(x)
                 }
                 """,
-            macros: ["JSSetter": JSSetterMacro.self],
-            indentationWidth: indentationWidth
+            macroSpecs: macroSpecs,
+            indentationWidth: indentationWidth,
         )
     }
 }
diff --git a/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/TestSupport.swift b/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/TestSupport.swift
new file mode 100644
index 00000000..84e34328
--- /dev/null
+++ b/Plugins/BridgeJS/Tests/BridgeJSMacrosTests/TestSupport.swift
@@ -0,0 +1,52 @@
+import SwiftSyntaxMacrosGenericTestSupport
+import Testing
+import SwiftSyntax
+import SwiftDiagnostics
+import SwiftSyntaxMacroExpansion
+
+enum TestSupport {
+    static func failureHandler(spec: TestFailureSpec) {
+        Issue.record(
+            Comment(rawValue: spec.message),
+            sourceLocation: .init(
+                fileID: spec.location.fileID,
+                filePath: spec.location.filePath,
+                line: spec.location.line,
+                column: spec.location.column
+            )
+        )
+    }
+
+    static func assertMacroExpansion(
+        _ originalSource: String,
+        expandedSource expectedExpandedSource: String,
+        diagnostics: [DiagnosticSpec] = [],
+        macroSpecs: [String: MacroSpec],
+        applyFixIts: [String]? = nil,
+        fixedSource expectedFixedSource: String? = nil,
+        testModuleName: String = "TestModule",
+        testFileName: String = "test.swift",
+        indentationWidth: Trivia = .spaces(4),
+        fileID: StaticString = #fileID,
+        filePath: StaticString = #filePath,
+        line: UInt = #line,
+        column: UInt = #column
+    ) {
+        SwiftSyntaxMacrosGenericTestSupport.assertMacroExpansion(
+            originalSource,
+            expandedSource: expectedExpandedSource,
+            diagnostics: diagnostics,
+            macroSpecs: macroSpecs,
+            applyFixIts: applyFixIts,
+            fixedSource: expectedFixedSource,
+            testModuleName: testModuleName,
+            testFileName: testFileName,
+            indentationWidth: indentationWidth,
+            failureHandler: TestSupport.failureHandler,
+            fileID: fileID,
+            filePath: filePath,
+            line: line,
+            column: column
+        )
+    }
+}