I would like to write a unit test for a generator function but I am not able to pass a properly mocked read stream (ReadStream) object.
Testable function:
public async *readChunks(file: string, chunkSize: number): AsyncIterableIterator<Buffer> {
if (!this.cwd) throw new Error('Working directory is not set!');
const readStream: ReadStream = fs.createReadStream(path.join(this.cwd, file), {
highWaterMark: chunkSize
});
for await (const chunk of readStream) yield chunk;
}
Failed implementation (I tried different mocking of the createReadStream but without success):
describe('Work Dir Utils', () => {
jest.mock('fs');
let workDirUtils: WorkDirUtils;
beforeEach(() => {
(os.tmpdir as jest.Mock).mockReturnValue('/tmp');
(fs.mkdtempSync as jest.Mock).mockReturnValue('/tmp/folder/pref-rand');
(fs.createReadStream as jest.Mock).mockReturnValue({});
workDirUtils = new WorkDirUtils();
workDirUtils.createTempDir('pref-');
});
afterEach(() => {
jest.clearAllMocks();
});
it('should read chunks of a file using generator', async () => {
for await (const chunk of workDirUtils.readChunks(
path.join(__dirname, './fixtures/manifest.ts'),
1024 * 1024 * 1024
)) {
expect(chunk).toBeInstanceOf(Buffer);
}
});
});
Any suggestions?
Actually, it turned out to be quite easy. In the end, I did not want to revoke the question. Maybe it will be useful for others.
jest.mock('fs');
jest.mock('tar');
jest.mock('os');
let workDirUtils: WorkDirUtils;
describe('Work Dir Utils', () => {
beforeEach(() => {
(os.tmpdir as jest.Mock).mockReturnValue('/tmp');
(fs.mkdtempSync as jest.Mock).mockReturnValue('/tmp/folder/pref-rand');
(fs.existsSync as jest.Mock).mockReturnValue(true);
(fs.createReadStream as jest.Mock).mockReturnValue(Readable.from([path.join(__dirname, './fixtures/manifest.ts')]));
workDirUtils = new WorkDirUtils();
workDirUtils.createTempDir('pref-');
});
afterEach(() => {
jest.clearAllMocks();
});
it('should generator function throw an error', async () => {
const workdirUtilsMock = new WorkDirUtils();
const generator = workdirUtilsMock.readChunks('file-path', 5000);
expect(generator.next).rejects.toThrow('Working directory is not set!');
});
it('should read chunks of a file using generator', async () => {
const generator = workDirUtils.readChunks(path.join(__dirname, './fixtures/manifest.ts'), 1024 * 1024 * 1024);
const response = await generator.next();
expect(response).toBeInstanceOf(Object);
expect(response.value).toEqual(path.join(__dirname, './fixtures/manifest.ts'));
});
});