test: add test for flushing buffers

Author: zirkelc

packages/logger/src/Logger.ts

@@ -876,17 +876,20 @@ class Logger extends Utility implements LoggerInterface {
     extraInput: LogItemExtraInput
   ): void {
     if (logLevel >= this.logLevel) {
-      const xRayTraceId = this.envVarsService.getXrayTraceId() as string;
-
-      // Print all log items in the context
-      if (this.#context[xRayTraceId]) {
-        for (const contextItem of this.#context[xRayTraceId]) {
-          this.printLog(...contextItem);
+      // Only flush buffer when log level is higher than the configured log level
+      if (logLevel > this.logLevel) {
+        const xRayTraceId = this.envVarsService.getXrayTraceId() as string;
+
+        // Print all log items in the context
+        if (this.#context[xRayTraceId]) {
+          for (const contextItem of this.#context[xRayTraceId]) {
+            this.printLog(...contextItem);
+          }
+
+          // Clear the context after flushing
+          // This also removes entries from other X-Ray trace IDs
+          this.#context = {};
         }
-
-        // Clear the context after flushing
-        // This also removes entries from other X-Ray trace IDs
-        this.#context = {};
       }
 
       if (this.#isInitialized) {

packages/logger/tests/unit/logFlushBuffer.test.ts

@@ -0,0 +1,84 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { Logger } from '../../src/Logger.js';
+import { LogLevel, LogLevelThreshold } from '../../src/constants.js';
+import type { ConfigServiceInterface } from '../../src/types/ConfigServiceInterface.js';
+import type {
+  LogFunction,
+  LogLevel as LogLevelType,
+} from '../../src/types/Logger.js';
+
+/**
+ * Helper function to get the console method for a given log level, we use this
+ * for properly mocking the console methods in the tests and account for the
+ * fact that `critical` is not a valid console method, which we proxy to `error`,
+ * and `trace` is internally proxied to `log`.
+ *
+ * @param method - The method to get the console method for
+ */
+const getConsoleMethod = (
+  method: string
+): keyof Omit<LogFunction, 'critical'> | 'log' => {
+  const lowercaseMethod = method.toLowerCase();
+  switch (lowercaseMethod) {
+    case 'trace':
+      return 'log';
+    case 'critical':
+      return 'error';
+    default:
+      return lowercaseMethod as keyof Omit<LogFunction, 'critical'>;
+  }
+};
+
+describe('Log flush buffer', () => {
+  const ENVIRONMENT_VARIABLES = process.env;
+
+  beforeEach(() => {
+    process.env = { ...ENVIRONMENT_VARIABLES, POWERTOOLS_DEV: 'true' };
+    vi.resetAllMocks();
+  });
+
+  it("doesn't flush buffer when calling a log level lower than the configured log level", () => {
+    // Prepare
+    const logger = new Logger({ logLevel: 'WARN' });
+
+    // Act
+    logger.debug('debug');
+    logger.info('info');
+
+    // Assess
+    expect(console.debug).not.toHaveBeenCalled();
+    expect(console.info).not.toHaveBeenCalled();
+  });
+
+  it("doesn't flush buffer when calling a log level equal to the configured log level", () => {
+    // Prepare
+    const logger = new Logger({ logLevel: 'WARN' });
+
+    // Act
+    logger.debug('debug');
+    logger.info('info');
+    logger.warn('warn');
+
+    // Assess
+    expect(console.debug).not.toHaveBeenCalled();
+    expect(console.info).not.toHaveBeenCalled();
+    expect(console.warn).toHaveBeenCalled();
+  });
+
+  it('flushes buffer when calling a log level higher than the configured log level', () => {
+    // Prepare
+    const logger = new Logger({ logLevel: 'WARN' });
+
+    // Act
+    logger.debug('debug');
+    logger.info('info');
+    logger.warn('warn');
+    logger.error('error');
+
+    // Assess
+    expect(console.debug).toHaveBeenCalled();
+    expect(console.info).toHaveBeenCalled();
+    expect(console.warn).toHaveBeenCalled();
+    expect(console.error).toHaveBeenCalled();
+  });
+});