sandbox = sinon.createSandbox(); fileStub = sandbox.stub(AwsEksDetector, 'fileAccessAsync' as any).resolves(true); Benchmark.js. The sandbox stub method can also be used to stub any kind of property. Due to this fact it's not viable to make it accept property descriptors as values, because then we wouldn't be able to know whether the user wants to pass a property descriptor or an simple object to replace that property. If you need to support very old runtimes that have incomplete support for ES5.1 you might get away with using loading es5-shim in your test environment. When I inspect the this.sandbox.loader function in the debugger it is correctly set to the stub. There should not be any issues with using Sinon v9.2.2 in newer versions of the same runtimes. Benchmark.js simplifies micro-benchmark testing on different components and their methods. Mocking Time with sinon.js – The Chronicles of Nerdia, There are situations where new Date() or Date.now is used in to remember how to mock/stub or spy on Date.now / new Date with Jest. Sinon sandbox makes stubbing much easier. Beware that this is inferred based on the value of the this object and the spy function’s prototype, so it may give false positives if you actively return the right kind of object. This behaves the same as spy.alwaysCalledWith(sinon.match(arg1), sinon.match(arg2), ...). I am writing this story to explain why it is not straight forward and what is the possible options or tools we can use to do that. Test 1 passes. Test 2 fails with: AssertionError: returned value is the fakedata from the stub. However it is not straight forward . Let's say we have this function that updates the database: Sinon.JS used to stub properties and methods in a sandbox. - stub-properties-and-methods-sinon.js spy.calledWithNew(); Returns true if spy/stub was called the new operator. Methods and properties are restored after test(s) are run. All we have to do is wrap the component around the declared object and call its methods. Here's the code we will test. Sinon will throw a very helpful error if the method you attempt to stub doesn’t exist. Sinon Stub API.returns (obj) - specify that whenever call Stub it will return the Object passed as param.throws - tells Sinon to throw general exception whenever given Stub is called.throws ("type") - tells Sinon to throw a particular type of exception whenever given Stub is called Checking the Order of Function Calls or Values Being Set. Wrapping a test with sinon.test() allows us to use Sinon’s sandboxing feature, allowing us to create spies, stubs and mocks via this.spy(), this.stub() and this.mock(). If you need to check that certain functions are called in order, you can use spies or stubs together with sinon.assert.callOrder: Sinon helps you create mocks, stubs and spies to help with unit testing. 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