test: Add direct unit tests for HealthRenderer

Covers control-char escaping (named and \u####), multi-dependency
ordering, and pass-through of non-ASCII characters — paths the handler
test only exercises indirectly.

Author: thced

src/test/java/com/retailsvc/http/internal/HealthRendererTest.java

@@ -0,0 +1,67 @@
+package com.retailsvc.http.internal;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.retailsvc.http.Dependency;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class HealthRendererTest {
+
+  @Test
+  void rendersUpWithNoDependencies() {
+    assertThat(HealthRenderer.renderJson(true, List.of()))
+        .isEqualTo("{\"outcome\":\"Up\",\"dependencies\":[]}");
+  }
+
+  @Test
+  void rendersDownWithNoDependencies() {
+    assertThat(HealthRenderer.renderJson(false, List.of()))
+        .isEqualTo("{\"outcome\":\"Down\",\"dependencies\":[]}");
+  }
+
+  @Test
+  void rendersSingleDependency() {
+    assertThat(HealthRenderer.renderJson(true, List.of(new Dependency("jdbc", true))))
+        .isEqualTo("{\"outcome\":\"Up\",\"dependencies\":[{\"id\":\"jdbc\",\"status\":\"Up\"}]}");
+  }
+
+  @Test
+  void rendersMultipleDependenciesInOrderWithCommaSeparators() {
+    List<Dependency> deps = List.of(new Dependency("jdbc", true), new Dependency("redis", false));
+    assertThat(HealthRenderer.renderJson(false, deps))
+        .isEqualTo(
+            "{\"outcome\":\"Down\",\"dependencies\":["
+                + "{\"id\":\"jdbc\",\"status\":\"Up\"},"
+                + "{\"id\":\"redis\",\"status\":\"Down\"}]}");
+  }
+
+  @Test
+  void escapesQuoteAndBackslashInId() {
+    assertThat(HealthRenderer.renderJson(true, List.of(new Dependency("a\"b\\c", true))))
+        .isEqualTo(
+            "{\"outcome\":\"Up\",\"dependencies\":[{\"id\":\"a\\\"b\\\\c\",\"status\":\"Up\"}]}");
+  }
+
+  @Test
+  void escapesNamedControlCharsInId() {
+    assertThat(HealthRenderer.renderJson(true, List.of(new Dependency("\b\f\n\r\t", true))))
+        .isEqualTo(
+            "{\"outcome\":\"Up\",\"dependencies\":[{\"id\":\"\\b\\f\\n"
+                + "\\r"
+                + "\\t\",\"status\":\"Up\"}]}");
+  }
+
+  @Test
+  void escapesUnnamedControlCharsAsHexUnicode() {
+    assertThat(HealthRenderer.renderJson(true, List.of(new Dependency("
", true))))
+        .isEqualTo(
+            "{\"outcome\":\"Up\",\"dependencies\":[{\"id\":\"\\u0001\\u001f\",\"status\":\"Up\"}]}");
+  }
+
+  @Test
+  void passesThroughNonAsciiCharactersVerbatim() {
+    assertThat(HealthRenderer.renderJson(true, List.of(new Dependency("café-é", true))))
+        .isEqualTo("{\"outcome\":\"Up\",\"dependencies\":[{\"id\":\"café-é\",\"status\":\"Up\"}]}");
+  }
+}