Compatibility test ApiResponse

- Remove redundant ApiResponseDiffTest. Comment regarding original issue retained.

Author: westse

core/src/test/java/org/openapitools/openapidiff/core/backcompat/ApiResponseBCTest.java

@@ -0,0 +1,26 @@
+package org.openapitools.openapidiff.core.backcompat;
+
+import static org.openapitools.openapidiff.core.TestUtils.assertOpenApiBackwardIncompatible;
+import static org.openapitools.openapidiff.core.TestUtils.assertSpecChangedButCompatible;
+import static org.openapitools.openapidiff.core.TestUtils.assertSpecUnchanged;
+
+import org.junit.jupiter.api.Test;
+
+public class ApiResponseBCTest {
+  private final String BASE = "bc_response_apiresponse_base.yaml";
+
+  @Test
+  public void unchanged() {
+    assertSpecUnchanged(BASE, BASE);
+  }
+
+  @Test
+  public void changedButCompatible() {
+    assertSpecChangedButCompatible(BASE, "bc_response_apiresponse_changed_but_compatible.yaml");
+  }
+
+  @Test
+  public void decreased() {
+    assertOpenApiBackwardIncompatible(BASE, "bc_response_apiresponse_decreased.yaml");
+  }
+}

core/src/test/java/org/openapitools/openapidiff/core/compare/ApiResponseDiffTest.java

@@ -0,0 +1,18 @@
+openapi: 3.0.0
+info:
+  description: myDesc
+  title: myTitle
+  version: 1.0.0
+paths:
+  /widgets:
+    get:
+      operationId: listWidgets
+      responses:
+        '200':
+          description: successful operation
+        '400':
+          description: Invalid status value
+  /widgets/index:
+    post:
+      operationId: indexWidgets
+      description: Regression test for https://github.com/OpenAPITools/openapi-diff/pull/206 (handle missing responses)

core/src/test/resources/backwardCompatibility/apiResponse_diff_1.yaml

@@ -0,0 +1,22 @@
+openapi: 3.0.0
+info:
+  description: myDesc
+  title: myTitle
+  version: 1.0.0
+paths:
+  /widgets:
+    get:
+      operationId: listWidgets
+      responses:
+        '200':
+          description: successful operation
+        '201':
+          description: OK
+        '400':
+          description: Invalid status value
+  /widgets/index:
+    post:
+      operationId: indexWidgets
+      responses:
+        '200':
+          description: successful operation

core/src/test/resources/backwardCompatibility/apiResponse_diff_2.yaml

@@ -0,0 +1,16 @@
+openapi: 3.0.0
+info:
+  description: myDesc
+  title: myTitle
+  version: 1.0.0
+paths:
+  /widgets:
+    get:
+      operationId: listWidgets
+      responses:
+        '200':
+          description: successful operation
+  /widgets/index:
+    post:
+      operationId: indexWidgets
+      description: Regression test for https://github.com/OpenAPITools/openapi-diff/pull/206 (handle missing responses)