test: add AnyOf diff test cases for schema validation

Author: DrSatyr

core/src/test/java/org/openapitools/openapidiff/core/SchemaDiffTest.java

@@ -352,4 +352,32 @@ public void changePatternHandling() {
     assertThat(props.get("patternAdded").getPattern().getNewPattern())
         .isEqualTo("^\\d{3}-\\d{2}-\\d{4}$?");
   }
+
+  @Test // issue #212
+  public void testAnyOfDiff() {
+    ChangedOpenApi changedOpenApi =
+        OpenApiCompare.fromLocations(
+            "schemaDiff/anyOf-diff-1.yaml", "schemaDiff/anyOf-diff-2.yaml");
+    ChangedSchema changedSchema =
+        getRequestBodyChangedSchema(changedOpenApi, POST, "/anyof/test", "application/json");
+
+    assertThat(changedSchema).isNotNull();
+    // The diff compares the *merged* schema resulting from anyOf, not the anyOf structure itself.
+    // See details in #772
+    assertThat(changedSchema.isChanged()).isEqualTo(DiffResult.COMPATIBLE);
+
+    // fieldA only changed required status, not its schema
+    assertThat(changedSchema.getChangedProperties()).isEmpty();
+
+    // fieldB: Removed from the merged schema properties
+    assertThat(changedSchema.getMissingProperties()).containsKey("fieldB");
+
+    // fieldC: Added to the merged schema properties
+    assertThat(changedSchema.getIncreasedProperties()).containsKey("fieldC");
+
+    // Check the overall required list changes for the merged schema
+    assertThat(changedSchema.getRequired().isChanged()).isEqualTo(DiffResult.COMPATIBLE);
+    assertThat(changedSchema.getRequired().getMissing()).containsExactly("fieldA");
+    assertThat(changedSchema.getRequired().getIncreased()).isEmpty();
+  }
 }

core/src/test/resources/schemaDiff/anyOf-diff-1.yaml

@@ -0,0 +1,35 @@
+openapi: 3.0.0
+info:
+  title: AnyOf Diff Test - Version 1
+  version: 1.0.0
+paths:
+  /anyof/test:
+    post:
+      summary: Test endpoint for anyOf diff
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              anyOf:
+                - $ref: '#/components/schemas/TypeA'
+                - $ref: '#/components/schemas/TypeB'
+      responses:
+        '200':
+          description: OK
+components:
+  schemas:
+    TypeA:
+      type: object
+      properties:
+        fieldA:
+          type: string
+        commonField:
+          type: integer
+      required:
+        - fieldA
+    TypeB:
+      type: object
+      properties:
+        fieldB:
+          type: boolean

core/src/test/resources/schemaDiff/anyOf-diff-2.yaml

@@ -0,0 +1,33 @@
+openapi: 3.0.0
+info:
+  title: AnyOf Diff Test - Version 2
+  version: 1.0.0
+paths:
+  /anyof/test:
+    post:
+      summary: Test endpoint for anyOf diff
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              anyOf:
+                - $ref: '#/components/schemas/TypeA'
+                - $ref: '#/components/schemas/TypeC'
+      responses:
+        '200':
+          description: OK
+components:
+  schemas:
+    TypeA:
+      type: object
+      properties:
+        fieldA:
+          type: string
+        commonField:
+          type: integer
+    TypeC:
+      type: object
+      properties:
+        fieldC:
+          type: number