Add a test for the support of external schemas in the router

Signed-off-by: David Festal <dfestal@redhat.com>

plugins/app-backend/src/service/__fixtures__/app-dir/dist/.config-schema.json

@@ -0,0 +1,4 @@
+{
+  "backstageConfigSchemaVersion": 1,
+  "schemas": []
+}

plugins/app-backend/src/service/router.test.ts

@@ -15,12 +15,13 @@
  */
 
 import { getVoidLogger } from '@backstage/backend-common';
-import { ConfigReader } from '@backstage/config';
+import { AppConfig, ConfigReader } from '@backstage/config';
 import express from 'express';
 import Router from 'express-promise-router';
 import { resolve as resolvePath } from 'path';
 import request from 'supertest';
 import { createRouter } from './router';
+import { loadConfigSchema } from '@backstage/config-loader';
 
 jest.mock('../lib/config', () => ({
   injectConfig: jest.fn(),
@@ -115,3 +116,75 @@ describe('createRouter with static fallback handler', () => {
     expect(response3.status).toBe(404);
   });
 });
+
+describe('createRouter config schema test', () => {
+  const libConfigs = require('../lib/config');
+  const libConfigsActual = jest.requireActual('../lib/config');
+  const readConfigsMock: jest.Mock = libConfigs.readConfigs;
+
+  beforeEach(() => {
+    jest.resetAllMocks();
+    readConfigsMock.mockImplementation(libConfigsActual.readConfigs);
+  });
+
+  it('uses an external schema', async () => {
+    await createRouter({
+      logger: getVoidLogger(),
+      config: new ConfigReader({
+        test: 'value',
+      }),
+      appPackageName: 'example-app',
+      schema: await loadConfigSchema({
+        serialized: {
+          schemas: [
+            {
+              value: {
+                type: 'object',
+                properties: {
+                  test: {
+                    visibility: 'frontend',
+                    type: 'string',
+                  },
+                },
+              },
+              path: '/mock',
+            },
+          ],
+          backstageConfigSchemaVersion: 1,
+        },
+      }),
+    });
+
+    const results = readConfigsMock.mock.results;
+    expect(results.length).toBe(1);
+
+    const mockedResult = results[0];
+    expect(mockedResult.type).toBe('return');
+    const result = await (mockedResult.value as Promise<AppConfig[]>);
+
+    expect(result.length).toBe(1);
+    expect(result[0].data).toStrictEqual({
+      test: 'value',
+    });
+  });
+
+  it('uses no external schema', async () => {
+    await createRouter({
+      logger: getVoidLogger(),
+      config: new ConfigReader({
+        test: 'value',
+      }),
+      appPackageName: 'example-app',
+    });
+
+    const results = readConfigsMock.mock.results;
+    expect(results.length).toBe(1);
+
+    const mockedResult = results[0];
+    expect(mockedResult.type).toBe('return');
+    const result = await (mockedResult.value as Promise<AppConfig[]>);
+
+    expect(result.length).toBe(1);
+    expect(result[0].data).toStrictEqual({});
+  });
+});