I see sandboxing is an option but I do not see how you can use a sandbox for this. Sinon will throw a very helpful error if the method you attempt to stub doesn’t exist. There should not be any issues with using Sinon v9.2.2 in newer versions of the same runtimes. - stub-properties-and-methods-sinon.js Test 1 passes. spy.calledWithNew(); Returns true if spy/stub was called the new operator. 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. The log messages show that it has printed the data from the file rather than the fakedata. However it is not straight forward . Checking the Order of Function Calls or Values Being Set. Methods and properties are restored after test(s) are run. Without it, the stub may be left in place and it may cause problems in other tests. When I inspect the this.sandbox.loader function in the debugger it is correctly set to the stub. Sinon.JS used to stub properties and methods in a sandbox. 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. Let's say we have this function that updates the database: This behaves the same as spy.alwaysCalledWith(sinon.match(arg1), sinon.match(arg2), ...). 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(). 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. Here's the code we will test. Is that possible? 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. This will avoid writing unit tests that pass if the code is using non-existent methods: sandbox = sinon.createSandbox(); fileStub = sandbox.stub(AwsEksDetector, 'fileAccessAsync' as any).resolves(true); Benchmark.js. Sinon sandbox makes stubbing much easier. The sandbox stub method can also be used to stub any kind of property. It is best practice to stub the method you expect to use on the same type of object you use in your code. If you need to check that certain functions are called in order, you can use spies or stubs together with sinon.assert.callOrder: Well, yes. Benchmark.js simplifies micro-benchmark testing on different components and their methods. 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