Examples for using mocked interfaces in tests

package.json

@@ -52,6 +52,7 @@
     "eslint-config-prettier": "^9.1.0",
     "jest": "^29.7.0",
     "jest-extended": "^4.0.2",
+    "jest-mock-extended": "^3.0.7",
     "opener": "^1.5.2",
     "prettier": "^3.2.4",
     "ts-jest": "^29.1.2",

test/loader/BasePackageLoader.test.ts

@@ -0,0 +1,125 @@
+import path from 'path';
+import { mock, mockReset } from 'jest-mock-extended';
+import { Readable } from 'stream';
+import { BasePackageLoader } from '../../src/loader/BasePackageLoader';
+import { LoadStatus } from '../../src/loader/PackageLoader';
+import { PackageDB } from '../../src/db';
+import { PackageCache } from '../../src/cache';
+import { RegistryClient } from '../../src/registry';
+import { CurrentBuildClient } from '../../src/current';
+import { loggerSpy } from '../testhelpers';
+
+describe('BasePackageLoader', () => {
+  let loader: BasePackageLoader;
+  const packageDBMock = mock<PackageDB>();
+  const packageCacheMock = mock<PackageCache>();
+  const registryClientMock = mock<RegistryClient>();
+  const currentBuildClientMock = mock<CurrentBuildClient>();
+
+  beforeEach(() => {
+    loggerSpy.reset();
+    mockReset(packageDBMock);
+    mockReset(packageCacheMock);
+    mockReset(registryClientMock);
+    mockReset(currentBuildClientMock);
+    loader = new BasePackageLoader(
+      packageDBMock,
+      packageCacheMock,
+      registryClientMock,
+      currentBuildClientMock,
+      { log: loggerSpy.log }
+    );
+  });
+
+  describe('#loadPackage', () => {
+    it('should return LOADED when the package is already loaded', async () => {
+      // set up the needed mocks and spys
+      loader.getPackageLoadStatus = jest.fn().mockReturnValue(LoadStatus.LOADED);
+
+      // call loadPackage
+      const result = await loader.loadPackage('some.ig', '1.2.3');
+
+      // check the expected result
+      expect(result).toBe(LoadStatus.LOADED);
+
+      // check the mocked function was called as expected
+      expect(loader.getPackageLoadStatus).toHaveBeenCalledWith('some.ig', '1.2.3');
+
+      // check that it didn't try to save it to the db again
+      expect(packageDBMock.savePackageInfo).not.toHaveBeenCalled();
+    });
+
+    it('should load a versioned package from the registry when it is not in the cache', async () => {
+      // set up the needed mocks and spys
+      // note -- this is the long way, which also mocks out all the calls happening inside the
+      // private this.loadPackageFromCache function. See other approach in next test.
+      // also note -- you could put a lot of this setup in a separate function so you don't
+      // need to call it in every test case (for the stuff in common between test cases).
+      const name = 'some.ig';
+      const version = '1.2.3';
+      const packagePath = path.resolve('path', 'to', `${name}-${version}`);
+      const packageJSONPath = path.resolve(packagePath, 'package.json');
+      const tarball = Readable.from([`${name}#${version}-data`]);
+      loader.getPackageLoadStatus = jest.fn().mockReturnValue(LoadStatus.NOT_LOADED);
+      packageCacheMock.isPackageInCache
+        .calledWith(name, version)
+        .mockReturnValueOnce(false) // on first call it's not in the cache
+        .mockReturnValueOnce(true); // on second call it is in the cache
+      registryClientMock.download.calledWith(name, version).mockResolvedValue(tarball);
+      packageCacheMock.cachePackageTarball
+        .calledWith(name, version, tarball)
+        .mockResolvedValue(packagePath);
+      packageCacheMock.getPackagePath.calledWith(name, version).mockReturnValue(packagePath);
+      packageCacheMock.getPackageJSONPath
+        .calledWith(name, version)
+        .mockReturnValue(packageJSONPath);
+      packageCacheMock.getPotentialResourcePaths.calledWith(name, version).mockReturnValue([]);
+      packageDBMock.getPackageStats
+        .calledWith(name, version)
+        .mockReturnValue({ name, version, resourceCount: 5 });
+
+      // call loadPackage
+      const result = await loader.loadPackage('some.ig', '1.2.3');
+
+      // check the expected result and log
+      expect(result).toBe(LoadStatus.LOADED);
+      expect(loggerSpy.getLastMessage('info')).toBe('Loaded some.ig#1.2.3 with 5 resources');
+
+      // check the package info was saved as expected
+      expect(packageDBMock.savePackageInfo).toHaveBeenCalledWith({
+        name: 'some.ig',
+        version: '1.2.3',
+        packagePath,
+        packageJSONPath
+      });
+    });
+  });
+
+  it('approach 2: should load a versioned package from the registry when it is not in the cache', async () => {
+    // set up the needed mocks and spys
+    // note -- this simplifies things a bit by mocking out the loader's private functions,
+    // but you probably will additionally want tests that do actually allow those functions
+    // to be fully executed (like demonstrated above). But you don't need to go through that
+    // whole rigamarole for every test; hence this approach.
+    const name = 'some.ig';
+    const version = '1.2.3';
+    const tarball = Readable.from([`${name}$${version}-data`]);
+    loader.getPackageLoadStatus = jest.fn().mockReturnValue(LoadStatus.NOT_LOADED);
+    packageCacheMock.isPackageInCache.calledWith(name, version).mockReturnValueOnce(false); // on first call it's not in the cache
+    registryClientMock.download.calledWith(name, version).mockResolvedValue(tarball);
+    // just mock out the private loadPackageFromCache function, saving us a lot of hassle
+    const loadPackageFromCacheSpy = jest
+      .spyOn(BasePackageLoader.prototype as any, 'loadPackageFromCache')
+      .mockReturnValue({ name, version, resourceCount: 5 });
+
+    // call loadPackage
+    const result = await loader.loadPackage('some.ig', '1.2.3');
+
+    // check the expected result and log
+    expect(result).toBe(LoadStatus.LOADED);
+    expect(loggerSpy.getLastMessage('info')).toBe('Loaded some.ig#1.2.3 with 5 resources');
+
+    // check the private loadPackageFromCache was called as expected
+    expect(loadPackageFromCacheSpy).toHaveBeenCalledWith('some.ig', '1.2.3');
+  });
+});