make test independent from side effects

Reviewed By: jeanlauliac

Differential Revision: D4939025

fbshipit-source-id: cc7f811484cba0db4df394edef294cabe7343c8b

packager/src/Bundler/__tests__/Bundler-test.js

@@ -359,15 +359,25 @@ describe('Bundler', function() {
         ]));
     });
 
-    it('return correct number of workers', () => {
-      os.cpus.mockReturnValue({length: 1});
-      expect(Bundler.getMaxWorkerCount()).toBe(1);
-      os.cpus.mockReturnValue({length: 8});
-      expect(Bundler.getMaxWorkerCount()).toBe(6);
-      os.cpus.mockReturnValue({length: 24});
-      expect(Bundler.getMaxWorkerCount()).toBe(14);
-      process.env.REACT_NATIVE_MAX_WORKERS = 5;
-      expect(Bundler.getMaxWorkerCount()).toBe(5);
+    describe('number of workers', () => {
+      beforeEach(() => {
+        delete process.env.REACT_NATIVE_MAX_WORKERS;
+      });
+
+      afterEach(() => {
+        delete process.env.REACT_NATIVE_MAX_WORKERS;
+      });
+
+      it('return correct number of workers', () => {
+        os.cpus.mockReturnValue({length: 1});
+        expect(Bundler.getMaxWorkerCount()).toBe(1);
+        os.cpus.mockReturnValue({length: 8});
+        expect(Bundler.getMaxWorkerCount()).toBe(6);
+        os.cpus.mockReturnValue({length: 24});
+        expect(Bundler.getMaxWorkerCount()).toBe(14);
+        process.env.REACT_NATIVE_MAX_WORKERS = 5;
+        expect(Bundler.getMaxWorkerCount()).toBe(5);
+      });
     });
   });
 });