add suggested tests

Author: lobsterkatie

packages/tracing/test/hub.test.ts

@@ -9,6 +9,7 @@ import { addExtensionMethods } from '../src/hubextensions';
 
 addExtensionMethods();
 
+const mathRandom = jest.spyOn(Math, 'random');
 describe('Hub', () => {
   beforeEach(() => {
     jest.spyOn(logger, 'warn');
@@ -178,6 +179,24 @@ describe('Hub', () => {
         expect(tracesSampler).toHaveBeenCalled();
       });
 
+      it('should set sampled = false if tracesSampler returns 0', () => {
+        const tracesSampler = jest.fn().mockReturnValue(0);
+        const hub = new Hub(new BrowserClient({ tracesSampler }));
+        const transaction = hub.startTransaction({ name: 'dogpark' });
+
+        expect(tracesSampler).toHaveBeenCalled();
+        expect(transaction.sampled).toBe(false);
+      });
+
+      it('should set sampled = true if tracesSampler returns 1', () => {
+        const tracesSampler = jest.fn().mockReturnValue(1);
+        const hub = new Hub(new BrowserClient({ tracesSampler }));
+        const transaction = hub.startTransaction({ name: 'dogpark' });
+
+        expect(tracesSampler).toHaveBeenCalled();
+        expect(transaction.sampled).toBe(true);
+      });
+
       it('should prefer tracesSampler to tracesSampleRate', () => {
         // make the two options do opposite things to prove precedence
         const tracesSampler = jest.fn().mockReturnValue(true);
@@ -296,7 +315,24 @@ describe('Hub', () => {
         // TODO fix this and write the test
       });
 
-      it("should inherit parent's sampling decision when creating a new transaction if tracesSampler is undefined", () => {
+      it("should inherit parent's positive sampling decision if tracesSampler is undefined", () => {
+        // we know that without inheritance  we'll get sampled = false (since our "random" number won't be below the
+        // sample rate), so make parent's decision the opposite to prove that inheritance takes precedence over
+        // tracesSampleRate
+        mathRandom.mockReturnValueOnce(1);
+        const hub = new Hub(new BrowserClient({ tracesSampleRate: 0.5 }));
+        const parentSamplingDecsion = true;
+
+        const transaction = hub.startTransaction({
+          name: 'dogpark',
+          parentSpanId: '12312012',
+          parentSampled: parentSamplingDecsion,
+        });
+
+        expect(transaction.sampled).toBe(parentSamplingDecsion);
+      });
+
+      it("should inherit parent's negative sampling decision if tracesSampler is undefined", () => {
         // tracesSampleRate = 1 means every transaction should end up with sampled = true, so make parent's decision the
         // opposite to prove that inheritance takes precedence over tracesSampleRate
         const hub = new Hub(new BrowserClient({ tracesSampleRate: 1 }));
@@ -311,7 +347,7 @@ describe('Hub', () => {
         expect(transaction.sampled).toBe(parentSamplingDecsion);
       });
 
-      it("should ignore parent's sampling decision when tracesSampler is defined", () => {
+      it("should ignore parent's positive sampling decision when tracesSampler is defined", () => {
         // this tracesSampler causes every transaction to end up with sampled = true, so make parent's decision the
         // opposite to prove that tracesSampler takes precedence over inheritance
         const tracesSampler = () => true;
@@ -327,6 +363,23 @@ describe('Hub', () => {
 
         expect(transaction.sampled).not.toBe(parentSamplingDecsion);
       });
+
+      it("should ignore parent's negative sampling decision when tracesSampler is defined", () => {
+        // this tracesSampler causes every transaction to end up with sampled = false, so make parent's decision the
+        // opposite to prove that tracesSampler takes precedence over inheritance
+        const tracesSampler = () => false;
+        const parentSamplingDecsion = true;
+
+        const hub = new Hub(new BrowserClient({ tracesSampler }));
+
+        const transaction = hub.startTransaction({
+          name: 'dogpark',
+          parentSpanId: '12312012',
+          parentSampled: parentSamplingDecsion,
+        });
+
+        expect(transaction.sampled).not.toBe(parentSamplingDecsion);
+      });
     });
   });
 });