Add createTestEntityPage utility for testing entity extensions

This adds a test utility that simplifies testing entity cards and content
extensions in the new frontend system. The utility creates a test page
that provides EntityProvider context and accepts entity extensions through
input redirects.

Also adds the `apis` option to `renderTestApp` for API overrides, and
includes tests for entity cards in catalog, org, and api-docs plugins.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/api-docs/src/alpha.test.tsx

@@ -0,0 +1,173 @@
+/*
+ * Copyright 2025 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { screen } from '@testing-library/react';
+import { renderTestApp } from '@backstage/frontend-test-utils';
+import { ApiEntity, ComponentEntity } from '@backstage/catalog-model';
+import { createTestEntityPage } from '@backstage/plugin-catalog-react/testUtils';
+import apiDocsPlugin from './alpha';
+
+const apiDocsDefinitionEntityCard = apiDocsPlugin.getExtension(
+  'entity-card:api-docs/definition',
+);
+const apiDocsDefinitionEntityContent = apiDocsPlugin.getExtension(
+  'entity-content:api-docs/definition',
+);
+const apiDocsConfigApi = apiDocsPlugin.getExtension('api:api-docs/config');
+
+describe('api-docs plugin entity extensions', () => {
+  describe('apiDocsDefinitionEntityCard', () => {
+    it('should render for API entities', async () => {
+      const entity: ApiEntity = {
+        apiVersion: 'backstage.io/v1alpha1',
+        kind: 'API',
+        metadata: {
+          name: 'my-api',
+          title: 'My API',
+        },
+        spec: {
+          type: 'openapi',
+          lifecycle: 'production',
+          owner: 'team-a',
+          definition:
+            'openapi: 3.0.0\ninfo:\n  title: My API\n  version: 1.0.0',
+        },
+      };
+
+      renderTestApp({
+        extensions: [
+          createTestEntityPage({ entity }),
+          apiDocsConfigApi,
+          apiDocsDefinitionEntityCard,
+        ],
+      });
+
+      expect(await screen.findByText('My API')).toBeInTheDocument();
+    });
+
+    it('should not render for non-API entities', async () => {
+      const entity: ComponentEntity = {
+        apiVersion: 'backstage.io/v1alpha1',
+        kind: 'Component',
+        metadata: {
+          name: 'my-component',
+        },
+        spec: {
+          type: 'service',
+          lifecycle: 'production',
+          owner: 'team-a',
+        },
+      };
+
+      renderTestApp({
+        extensions: [
+          createTestEntityPage({ entity }),
+          apiDocsConfigApi,
+          apiDocsDefinitionEntityCard,
+        ],
+      });
+
+      // Wait for page to render, then check definition card is not shown
+      expect(await screen.findByText('my-component')).toBeInTheDocument();
+      expect(screen.queryByText('openapi')).not.toBeInTheDocument();
+    });
+
+    it('should display the API definition content', async () => {
+      const entity: ApiEntity = {
+        apiVersion: 'backstage.io/v1alpha1',
+        kind: 'API',
+        metadata: {
+          name: 'pet-api',
+        },
+        spec: {
+          type: 'openapi',
+          lifecycle: 'production',
+          owner: 'team-a',
+          definition: JSON.stringify({
+            openapi: '3.0.0',
+            info: { title: 'Pet Store API', version: '1.0.0' },
+          }),
+        },
+      };
+
+      renderTestApp({
+        extensions: [
+          createTestEntityPage({ entity }),
+          apiDocsConfigApi,
+          apiDocsDefinitionEntityCard,
+        ],
+      });
+
+      expect(await screen.findByText('pet-api')).toBeInTheDocument();
+    });
+  });
+
+  describe('apiDocsDefinitionEntityContent', () => {
+    it('should render for API entities', async () => {
+      const entity: ApiEntity = {
+        apiVersion: 'backstage.io/v1alpha1',
+        kind: 'API',
+        metadata: {
+          name: 'content-api',
+          title: 'Content API',
+        },
+        spec: {
+          type: 'graphql',
+          lifecycle: 'production',
+          owner: 'team-b',
+          definition: 'type Query { hello: String }',
+        },
+      };
+
+      renderTestApp({
+        extensions: [
+          createTestEntityPage({ entity }),
+          apiDocsConfigApi,
+          apiDocsDefinitionEntityContent,
+        ],
+      });
+
+      expect(await screen.findByText('Content API')).toBeInTheDocument();
+    });
+
+    it('should not render for non-API entities', async () => {
+      const entity: ComponentEntity = {
+        apiVersion: 'backstage.io/v1alpha1',
+        kind: 'Component',
+        metadata: {
+          name: 'my-service',
+        },
+        spec: {
+          type: 'service',
+          lifecycle: 'production',
+          owner: 'team-a',
+        },
+      };
+
+      renderTestApp({
+        extensions: [
+          createTestEntityPage({ entity }),
+          apiDocsConfigApi,
+          apiDocsDefinitionEntityContent,
+        ],
+      });
+
+      // Content should not render for Components
+      expect(await screen.findByText('my-service')).toBeInTheDocument();
+      expect(screen.queryByText('Definition')).not.toBeInTheDocument();
+    });
+  });
+});