feat(testing): Create TestingLogger

Useful for testing logging output from e2e tests or unit tests

packages/testing/src/index.ts

@@ -10,4 +10,5 @@ export * from './initializers/test-db-initializer';
 export * from './initializers/mysql-initializer';
 export * from './initializers/postgres-initializer';
 export * from './initializers/sqljs-initializer';
+export * from './testing-logger';
 export * from './types';

packages/testing/src/testing-logger.ts

@@ -0,0 +1,89 @@
+import { VendureLogger } from '@vendure/core';
+
+/**
+ * @description
+ * The TestingLogger can be used in unit tests or e2e tests to make assertions on whether the various
+ * Logger methods have been called, and which which arguments.
+ *
+ * Here's some examples of how to use it in e2e tests and unit tests. In both cases we are using
+ * the Jest testing framework, but the TestingLogger should work with other similar frameworks
+ * (e.g. replacing `jest.fn()` with `jasmine.createSpy()`).
+ *
+ * @example
+ * ```TypeScript
+ * // e2e test example
+ * import { createTestEnvironment, TestingLogger } from '\@vendure/testing';
+ *
+ * const testingLogger = new TestingLogger(() => jest.fn());
+ *
+ * const { server, adminClient, shopClient } = createTestEnvironment({
+ *   ...testConfig,
+ *   logger: testingLogger,
+ * });
+ *
+ * // e2e testing setup omitted
+ *
+ * it('should log an error', async () => {
+ *   // The `errorSpy` property exposes the Jest mock function
+ *   testingLogger.errorSpy.mockClear();
+ *
+ *   await doSomethingThatErrors();
+ *
+ *   expect(testingLogger.errorSpy).toHaveBeenCalled();
+ * });
+ * ```
+ *
+ * @example
+ * ```TypeScript
+ * // unit test example
+ * import { Test } from '\@nestjs/testing';
+ * import { Logger } from '\@vendure/core';
+ * import { TestingLogger } from '\@vendure/testing';
+ *
+ * beforeEach(async () => {
+ *   const moduleRef = await Test.createTestingModule({
+ *     // Nest testing setup omitted
+ *   }).compile();
+ *
+ *   Logger.useLogger(testingLogger);
+ *   moduleRef.useLogger(new Logger());
+ * }
+ * ```
+ *
+ * @docsCategory testing
+ */
+export class TestingLogger<Spy extends (...args: any[]) => any> implements VendureLogger {
+    constructor(private createSpyFn: () => Spy) {
+        this.debugSpy = createSpyFn();
+        this.errorSpy = createSpyFn();
+        this.infoSpy = createSpyFn();
+        this.verboseSpy = createSpyFn();
+        this.warnSpy = createSpyFn();
+    }
+
+    debugSpy: Spy;
+    errorSpy: Spy;
+    infoSpy: Spy;
+    verboseSpy: Spy;
+    warnSpy: Spy;
+
+    debug(message: string, context?: string): void {
+        this.debugSpy(message, context);
+    }
+
+    error(message: string, context?: string, trace?: string): void {
+        this.errorSpy(message, context, trace);
+    }
+
+    info(message: string, context?: string): void {
+        this.infoSpy(message, context);
+    }
+
+    verbose(message: string, context?: string): void {
+        this.verboseSpy(message, context);
+    }
+
+    warn(message: string, context?: string): void {
+        this.warnSpy(message, context);
+    }
+}