diff --git a/Cargo.lock b/Cargo.lock
index 5126167ca22..95ff171b7ac 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -376,6 +376,15 @@ dependencies = [
  "hashbrown",
 ]
 
+[[package]]
+name = "indoc"
+version = "2.0.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a37b2691796cffeb8a8cd305ac66e65841559f147f4e63231d0eafa4db5384d1"
+dependencies = [
+ "rustversion",
+]
+
 [[package]]
 name = "insta"
 version = "1.48.0"
@@ -585,6 +594,7 @@ dependencies = [
  "dirs",
  "getopts",
  "ignore",
+ "indoc",
  "insta",
  "itertools",
  "regex",
@@ -616,6 +626,12 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "rustversion"
+version = "1.0.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf54715a573b99ac80df0bc206da022bcd442c974952c7b9720069370852e21f"
+
 [[package]]
 name = "same-file"
 version = "1.0.6"
diff --git a/Cargo.toml b/Cargo.toml
index bf1474284ad..9b27c543197 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -61,6 +61,7 @@ rustfmt-config_proc_macro = { version = "0.3", path = "config_proc_macro" }
 semver = "1.0.21"
 
 [dev-dependencies]
+indoc = "2.0.8"
 tempfile = "3.23.0"
 insta = { version = "1.48.0", features = ["filters"] }
 
diff --git a/src/config/mod.rs b/src/config/mod.rs
index 141933cd7cf..2a51861920d 100644
--- a/src/config/mod.rs
+++ b/src/config/mod.rs
@@ -550,6 +550,7 @@ fn config_path(options: &dyn CliOptions) -> Result<Option<PathBuf>, Error> {
 #[cfg(test)]
 mod test {
     use super::*;
+    use indoc::formatdoc;
     use std::str;
 
     use crate::config::macro_names::{MacroName, MacroSelectors};
@@ -726,7 +727,10 @@ mod test {
         let toml = used_options.to_toml().unwrap();
         assert_eq!(
             toml,
-            format!("merge_derives = {merge_derives}\nskip_children = {skip_children}\n",)
+            formatdoc! {"
+                merge_derives = {merge_derives}
+                skip_children = {skip_children}
+            "}
         );
     }
 
diff --git a/src/emitter/checkstyle.rs b/src/emitter/checkstyle.rs
index c320c16bd1d..e1d8b44ce14 100644
--- a/src/emitter/checkstyle.rs
+++ b/src/emitter/checkstyle.rs
@@ -68,6 +68,7 @@ where
 #[cfg(test)]
 mod tests {
     use super::*;
+    use indoc::indoc;
     use std::path::PathBuf;
 
     #[test]
@@ -89,11 +90,27 @@ mod tests {
     #[test]
     fn emits_single_xml_tree_containing_all_files() {
         let bin_file = "src/bin.rs";
-        let bin_original = ["fn main() {", "println!(\"Hello, world!\");", "}"];
-        let bin_formatted = ["fn main() {", "    println!(\"Hello, world!\");", "}"];
+        let bin_original = indoc! {r#"
+            fn main() {
+            println!("Hello, world!");
+            }
+        "#};
+        let bin_formatted = indoc! {r#"
+            fn main() {
+                println!("Hello, world!");
+            }
+        "#};
         let lib_file = "src/lib.rs";
-        let lib_original = ["fn greet() {", "println!(\"Greetings!\");", "}"];
-        let lib_formatted = ["fn greet() {", "    println!(\"Greetings!\");", "}"];
+        let lib_original = indoc! {r#"
+            fn greet() {
+            println!("Greetings!");
+            }
+        "#};
+        let lib_formatted = indoc! {r#"
+            fn greet() {
+                println!("Greetings!");
+            }
+        "#};
         let mut writer = Vec::new();
         let mut emitter = CheckstyleEmitter::default();
         let _ = emitter.emit_header(&mut writer);
@@ -102,8 +119,8 @@ mod tests {
                 &mut writer,
                 FormattedFile {
                     filename: &FileName::Real(PathBuf::from(bin_file)),
-                    original_text: &bin_original.join("\n"),
-                    formatted_text: &bin_formatted.join("\n"),
+                    original_text: bin_original,
+                    formatted_text: bin_formatted,
                 },
             )
             .unwrap();
@@ -112,8 +129,8 @@ mod tests {
                 &mut writer,
                 FormattedFile {
                     filename: &FileName::Real(PathBuf::from(lib_file)),
-                    original_text: &lib_original.join("\n"),
-                    formatted_text: &lib_formatted.join("\n"),
+                    original_text: lib_original,
+                    formatted_text: lib_formatted,
                 },
             )
             .unwrap();
diff --git a/src/emitter/diff.rs b/src/emitter/diff.rs
index 4e48c59ea29..5f10f71b84d 100644
--- a/src/emitter/diff.rs
+++ b/src/emitter/diff.rs
@@ -51,6 +51,7 @@ impl Emitter for DiffEmitter {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use indoc::{formatdoc, indoc};
     use std::path::PathBuf;
 
     #[test]
@@ -75,11 +76,27 @@ mod tests {
     #[test]
     fn prints_file_names_when_config_is_enabled() {
         let bin_file = "src/bin.rs";
-        let bin_original = "fn main() {\nprintln!(\"Hello, world!\");\n}";
-        let bin_formatted = "fn main() {\n    println!(\"Hello, world!\");\n}";
+        let bin_original = indoc! {r#"
+            fn main() {
+            println!("Hello, world!");
+            }
+        "#};
+        let bin_formatted = indoc! {r#"
+            fn main() {
+                println!("Hello, world!");
+            }
+        "#};
         let lib_file = "src/lib.rs";
-        let lib_original = "fn greet() {\nprintln!(\"Greetings!\");\n}";
-        let lib_formatted = "fn greet() {\n    println!(\"Greetings!\");\n}";
+        let lib_original = indoc! {r#"
+            fn greet() {
+            println!("Greetings!");
+            }
+        "#};
+        let lib_formatted = indoc! {r#"
+            fn greet() {
+                println!("Greetings!");
+            }
+        "#};
 
         let mut writer = Vec::new();
         let mut config = Config::default();
@@ -108,7 +125,10 @@ mod tests {
 
         assert_eq!(
             String::from_utf8(writer).unwrap(),
-            format!("{bin_file}\n{lib_file}\n"),
+            formatdoc! {"
+                {bin_file}
+                {lib_file}
+            "},
         )
     }
 
diff --git a/src/emitter/json.rs b/src/emitter/json.rs
index 8c84ff72d04..bc15b424bde 100644
--- a/src/emitter/json.rs
+++ b/src/emitter/json.rs
@@ -106,6 +106,7 @@ impl JsonEmitter {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use indoc::indoc;
     use std::path::PathBuf;
 
     #[test]
@@ -122,7 +123,12 @@ mod tests {
                 expected_begin_line: 79,
                 expected_end_line: 82,
                 original: String::from("fn Foo<T>() where T: Bar {\n"),
-                expected: String::from("fn Foo<T>()\nwhere\n    T: Bar,\n{\n"),
+                expected: String::from(indoc! {"
+                    fn Foo<T>()
+                    where
+                        T: Bar,
+                    {
+                "}),
             }],
         };
         let mismatch = Mismatch {
@@ -213,32 +219,32 @@ mod tests {
     #[test]
     fn emits_array_with_files_with_diffs() {
         let file_name = "src/bin.rs";
-        let original = [
-            "fn main() {",
-            "println!(\"Hello, world!\");",
-            "}",
-            "",
-            "#[cfg(test)]",
-            "mod tests {",
-            "#[test]",
-            "fn it_works() {",
-            "    assert_eq!(2 + 2, 4);",
-            "}",
-            "}",
-        ];
-        let formatted = [
-            "fn main() {",
-            "    println!(\"Hello, world!\");",
-            "}",
-            "",
-            "#[cfg(test)]",
-            "mod tests {",
-            "    #[test]",
-            "    fn it_works() {",
-            "        assert_eq!(2 + 2, 4);",
-            "    }",
-            "}",
-        ];
+        let original = indoc! {r#"
+            fn main() {
+            println!("Hello, world!");
+            }
+
+            #[cfg(test)]
+            mod tests {
+            #[test]
+            fn it_works() {
+                assert_eq!(2 + 2, 4);
+            }
+            }
+        "#};
+        let formatted = indoc! {r#"
+            fn main() {
+                println!("Hello, world!");
+            }
+
+            #[cfg(test)]
+            mod tests {
+                #[test]
+                fn it_works() {
+                    assert_eq!(2 + 2, 4);
+                }
+            }
+        "#};
         let mut writer = Vec::new();
         let mut emitter = JsonEmitter::default();
         let _ = emitter.emit_header(&mut writer);
@@ -247,8 +253,8 @@ mod tests {
                 &mut writer,
                 FormattedFile {
                     filename: &FileName::Real(PathBuf::from(file_name)),
-                    original_text: &original.join("\n"),
-                    formatted_text: &formatted.join("\n"),
+                    original_text: original,
+                    formatted_text: formatted,
                 },
             )
             .unwrap();
@@ -269,9 +275,12 @@ mod tests {
                     original_end_line: 10,
                     expected_begin_line: 7,
                     expected_end_line: 10,
-                    original: String::from(
-                        "#[test]\nfn it_works() {\n    assert_eq!(2 + 2, 4);\n}\n",
-                    ),
+                    original: String::from(indoc! {"
+                        #[test]
+                        fn it_works() {
+                            assert_eq!(2 + 2, 4);
+                        }
+                    "}),
                     expected: String::from(
                         "    #[test]\n    fn it_works() {\n        assert_eq!(2 + 2, 4);\n    }\n",
                     ),
@@ -286,11 +295,27 @@ mod tests {
     #[test]
     fn emits_valid_json_with_multiple_files() {
         let bin_file = "src/bin.rs";
-        let bin_original = ["fn main() {", "println!(\"Hello, world!\");", "}"];
-        let bin_formatted = ["fn main() {", "    println!(\"Hello, world!\");", "}"];
+        let bin_original = indoc! {r#"
+            fn main() {
+            println!("Hello, world!");
+            }
+        "#};
+        let bin_formatted = indoc! {r#"
+            fn main() {
+                println!("Hello, world!");
+            }
+        "#};
         let lib_file = "src/lib.rs";
-        let lib_original = ["fn greet() {", "println!(\"Greetings!\");", "}"];
-        let lib_formatted = ["fn greet() {", "    println!(\"Greetings!\");", "}"];
+        let lib_original = indoc! {r#"
+            fn greet() {
+            println!("Greetings!");
+            }
+        "#};
+        let lib_formatted = indoc! {r#"
+            fn greet() {
+                println!("Greetings!");
+            }
+        "#};
         let mut writer = Vec::new();
         let mut emitter = JsonEmitter::default();
         let _ = emitter.emit_header(&mut writer);
@@ -299,8 +324,8 @@ mod tests {
                 &mut writer,
                 FormattedFile {
                     filename: &FileName::Real(PathBuf::from(bin_file)),
-                    original_text: &bin_original.join("\n"),
-                    formatted_text: &bin_formatted.join("\n"),
+                    original_text: bin_original,
+                    formatted_text: bin_formatted,
                 },
             )
             .unwrap();
@@ -309,8 +334,8 @@ mod tests {
                 &mut writer,
                 FormattedFile {
                     filename: &FileName::Real(PathBuf::from(lib_file)),
-                    original_text: &lib_original.join("\n"),
-                    formatted_text: &lib_formatted.join("\n"),
+                    original_text: lib_original,
+                    formatted_text: lib_formatted,
                 },
             )
             .unwrap();
diff --git a/src/rustfmt_diff.rs b/src/rustfmt_diff.rs
index 4624683fa05..1734f5c02d5 100644
--- a/src/rustfmt_diff.rs
+++ b/src/rustfmt_diff.rs
@@ -284,6 +284,7 @@ mod test {
     use super::DiffLine::*;
     use super::{Mismatch, make_diff};
     use super::{ModifiedChunk, ModifiedLines};
+    use indoc::indoc;
 
     #[test]
     fn diff_simple() {
@@ -370,7 +371,13 @@ mod test {
     fn modified_lines_from_str() {
         use std::str::FromStr;
 
-        let src = "1 6 2\nfn some() {}\nfn main() {}\n25 3 1\n  struct Test {}";
+        let src = indoc! {"
+            1 6 2
+            fn some() {}
+            fn main() {}
+            25 3 1
+              struct Test {}
+        "};
         let lines = ModifiedLines::from_str(src).unwrap();
         assert_eq!(
             lines,
diff --git a/src/test/mod.rs b/src/test/mod.rs
index c1007511126..7c27b7b8f8b 100644
--- a/src/test/mod.rs
+++ b/src/test/mod.rs
@@ -1,3 +1,4 @@
+use indoc::indoc;
 use std::collections::HashMap;
 use std::env;
 use std::fs;
@@ -619,7 +620,14 @@ fn stdin_formatting_smoke_test() {
     }
 
     #[cfg(not(windows))]
-    assert_eq!(buf, "<stdin>:\n\nfn main() {}\n".as_bytes());
+    {
+        let expected = indoc! {"
+            <stdin>:
+
+            fn main() {}
+        "};
+        assert_eq!(buf, expected.as_bytes());
+    }
     #[cfg(windows)]
     assert_eq!(buf, "<stdin>:\n\nfn main() {}\r\n".as_bytes());
 }
@@ -644,8 +652,19 @@ fn stdin_parser_panic_caught() {
 #[test]
 fn stdin_works_with_modified_lines() {
     init_log();
-    let input = "\nfn\n some( )\n{\n}\nfn main () {}\n";
-    let output = "1 6 2\nfn some() {}\nfn main() {}\n";
+    let input = indoc! {"
+
+        fn
+         some( )
+        {
+        }
+        fn main () {}
+    "};
+    let output = indoc! {"
+        1 6 2
+        fn some() {}
+        fn main() {}
+    "};
 
     let input = Input::Text(input.to_owned());
     let mut config = Config::default();
@@ -715,7 +734,10 @@ fn stdin_disable_all_formatting_test() {
 #[test]
 fn stdin_generated_files_issue_5172() {
     init_log();
-    let input = Input::Text("//@generated\nfn   main() {}".to_owned());
+    let input = Input::Text(String::from(indoc! {"
+        //@generated
+        fn   main() {}
+    "}));
     let mut config = Config::default();
     config.set().emit_mode(EmitMode::Stdout);
     config.set().format_generated_files(false);
@@ -729,7 +751,12 @@ fn stdin_generated_files_issue_5172() {
     // N.B. this should be changed once `format_generated_files` is supported with stdin
     assert_eq!(
         String::from_utf8(buf).unwrap(),
-        "<stdin>:\n\n//@generated\nfn main() {}\n",
+        indoc! {"
+            <stdin>:
+
+            //@generated
+            fn main() {}
+        "},
     );
 }
 
@@ -737,7 +764,11 @@ fn stdin_generated_files_issue_5172() {
 fn stdin_handles_mod_inner_ignore_attr() {
     // see https://github.com/rust-lang/rustfmt/issues/5368
     init_log();
-    let input = String::from("#![rustfmt::skip]\n\nfn    main() {  }");
+    let input = String::from(indoc! {"
+        #![rustfmt::skip]
+
+        fn    main() {  }
+    "});
     let mut child = Command::new(rustfmt().to_str().unwrap())
         .stdin(Stdio::piped())
         .stdout(Stdio::piped())
diff --git a/tests/cargo-fmt/main.rs b/tests/cargo-fmt/main.rs
index 63cc12521a8..f6da068aa95 100644
--- a/tests/cargo-fmt/main.rs
+++ b/tests/cargo-fmt/main.rs
@@ -1,5 +1,6 @@
 // Integration tests for cargo-fmt.
 
+use indoc::panicdoc;
 use std::env;
 use std::path::Path;
 use std::process::Command;
@@ -43,17 +44,17 @@ macro_rules! assert_that {
     ($args:expr, $check:ident $check_args:tt) => {
         let (stdout, stderr) = cargo_fmt($args);
         if !stdout.$check$check_args {
-            panic!(
-                "Output not expected for cargo-fmt {:?}\n\
-                 expected: {}{}\n\
-                 actual stdout:\n{}\n\
-                 actual stderr:\n{}",
-                $args,
-                stringify!($check),
-                stringify!($check_args),
-                stdout,
-                stderr
-            );
+            let args = $args;
+            let check = stringify!($check);
+            let check_args = stringify!($check_args);
+            panicdoc! {"
+                Output not expected for cargo-fmt {args:?}
+                expected: {check}{check_args}
+                actual stdout:
+                {stdout}
+                actual stderr:
+                {stderr}",
+            };
         }
     };
 }
diff --git a/tests/rustfmt/main.rs b/tests/rustfmt/main.rs
index e04fae7ad04..2220df2b617 100644
--- a/tests/rustfmt/main.rs
+++ b/tests/rustfmt/main.rs
@@ -1,5 +1,6 @@
 //! Integration tests for rustfmt.
 
+use indoc::panicdoc;
 use std::env;
 use std::fs::{File, remove_file};
 use std::path::Path;
@@ -45,16 +46,16 @@ macro_rules! assert_that {
     ($args:expr, $($check:ident $check_args:tt)&&+) => {
         let (stdout, stderr) = rustfmt($args);
         if $(!stdout.$check$check_args && !stderr.$check$check_args)||* {
-            panic!(
-                "Output not expected for rustfmt {:?}\n\
-                 expected: {}\n\
-                 actual stdout:\n{}\n\
-                 actual stderr:\n{}",
-                $args,
-                stringify!($( $check$check_args )&&*),
-                stdout,
-                stderr
-            );
+            let args = $args;
+            let expected = stringify!($( $check$check_args )&&*);
+            panicdoc! {"
+                Output not expected for rustfmt {args:?}
+                expected: {expected}
+                actual stdout:
+                {stdout}
+                actual stderr:
+                {stderr}",
+            };
         }
     };
 }