fix: wrong scope in captureMethod (#1026)

* Update Tracer.ts

using the captureMethod decorator the "this" is no longer the original obj so changing to the target fixes this

* added test to verify change to captureMethod.

* fix to code formting to pass tests

* reverted Tracer.ts and reedited for a clean commit

* issue with the last commit, fixing Tracter again

* fix lint issues

Author: ratscrew

Diff for: packages/tracer/src/Tracer.ts

@@ -424,7 +424,7 @@ class Tracer extends Utility implements TracerInterface {
         return this.provider.captureAsyncFunc(`### ${originalMethod.name}`, async subsegment => {          
           let result;
           try {
-            result = await originalMethod.apply(this, [...args]);
+            result = await originalMethod.apply(target, [...args]);
             this.addResponseAsMetadata(result, originalMethod.name);
           } catch (error) {
             this.addErrorAsMetadata(error as Error); 

Diff for: packages/tracer/tests/unit/Tracer.test.ts

@@ -973,6 +973,42 @@ describe('Class: Tracer', () => {
 
     });
 
+    test('when used as decorator and when calling other methods/props in the class they are called in the orginal scope', async () => {
+
+      // Prepare
+      const tracer: Tracer = new Tracer();
+      const newSubsegment: Segment | Subsegment | undefined = new Subsegment('### dummyMethod');
+      jest.spyOn(tracer.provider, 'getSegment')
+        .mockImplementation(() => newSubsegment);
+      setContextMissingStrategy(() => null);
+
+      class Lambda implements LambdaInterface {
+
+        @tracer.captureMethod()
+        // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+        // @ts-ignore
+        public async dummyMethod(): Promise<string> {
+          return `otherMethod:${this.otherMethod()}`;
+        }
+
+        @tracer.captureLambdaHandler()
+        // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+        // @ts-ignore
+        public async handler<TEvent, TResult>(_event: TEvent, _context: Context, _callback: Callback<TResult>): void | Promise<TResult> {
+          return <TResult>(await this.dummyMethod() as unknown);
+        }
+
+        public otherMethod(): string {
+          return 'otherMethod';
+        }
+
+      }
+
+      // Act / Assess
+      expect(await (new Lambda()).handler({}, context, () => console.log('Lambda invoked!'))).toEqual('otherMethod:otherMethod');
+
+    });
+
   });
 
   describe('Method: captureAWS', () => {