refactor(metrics): unit tests for Metrics are written to follow similar convention as Logger/Tracer

packages/metrics/src/Metrics.ts

@@ -2,6 +2,7 @@ import { Callback, Context, Handler } from 'aws-lambda';
 import { Utility } from '@aws-lambda-powertools/commons';
 import { MetricsInterface } from '.';
 import { ConfigServiceInterface, EnvironmentVariablesService } from './config';
+import { MAX_DIMENSION_COUNT, MAX_METRICS_SIZE, DEFAULT_NAMESPACE, COLD_START_METRIC } from './constants';
 import {
   MetricsOptions,
   Dimensions,
@@ -16,10 +17,6 @@ import {
   StoredMetric,
 } from './types';
 
-const MAX_METRICS_SIZE = 100;
-const MAX_DIMENSION_COUNT = 29;
-const DEFAULT_NAMESPACE = 'default_namespace';
-
 /**
  * ## Intro
  * Metrics creates custom metrics asynchronously by logging metrics to standard output following Amazon CloudWatch Embedded Metric Format (EMF).
@@ -228,7 +225,7 @@ class Metrics extends Utility implements MetricsInterface {
     if (this.functionName != null) {
       singleMetric.addDimension('function_name', this.functionName);
     }
-    singleMetric.addMetric('ColdStart', MetricUnits.Count, 1);
+    singleMetric.addMetric(COLD_START_METRIC, MetricUnits.Count, 1);
   }
 
   public clearDefaultDimensions(): void {

packages/metrics/src/constants.ts

@@ -0,0 +1,4 @@
+export const COLD_START_METRIC = 'ColdStart';
+export const DEFAULT_NAMESPACE = 'default_namespace';
+export const MAX_METRICS_SIZE = 100;
+export const MAX_DIMENSION_COUNT = 29;

packages/metrics/tests/helpers/metricsUtils.ts

@@ -1,5 +1,9 @@
 import { CloudWatch } from 'aws-sdk';
 import promiseRetry from 'promise-retry';
+import { Metrics } from '../../src';
+import { ExtraOptions, MetricUnits } from '../../src/types';
+import { Context, Handler } from 'aws-lambda';
+import { LambdaInterface } from '@aws-lambda-powertools/commons';
 
 const getMetrics = async (cloudWatchClient: CloudWatch, namespace: string, metric: string, expectedMetrics: number): Promise<CloudWatch.ListMetricsOutput> => {
   const retryOptions = { retries: 20, minTimeout: 5_000, maxTimeout: 10_000, factor: 1.25 };
@@ -21,4 +25,27 @@ const getMetrics = async (cloudWatchClient: CloudWatch, namespace: string, metri
   }, retryOptions);
 };
 
-export { getMetrics };
+const setupDecoratorLambdaHandler = (metrics: Metrics, options: ExtraOptions = {}): Handler => {
+
+  class LambdaFunction implements LambdaInterface {
+    @metrics.logMetrics(options)
+    // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+    // @ts-ignore
+    public async handler<TEvent>(_event: TEvent, _context: Context): Promise<string> {
+      metrics.addMetric('decorator-lambda-test-metric', MetricUnits.Count, 1);
+
+      return 'Lambda invoked!';
+    }
+  }
+
+  const handlerClass = new LambdaFunction();
+  const handler = handlerClass.handler.bind(handlerClass);
+
+  return handler;
+};
+
+export {
+  getMetrics,
+  setupDecoratorLambdaHandler
+};
+