#jest #testing #javascript #nodeJest set, clear and reset mock/spy/stub implementationBetween test runs we need mocked/spied on imports and functions to be reset so that assertions don’t fail due to stale calls (from a previous test). This is a way to mitigate what little statefulness is in the system. In unit tests of complex systems, it’s not always ...
#jest #testing #javascript #nodeJest .fn() and .spyOn() spy/stub/mock assertion referenceWhere other JavaScript testing libraries would lean on a specific stub/spy library like Sinon - Standalone test spies, stubs and mocks for JavaScript. Works with any unit testing framework., Jest comes with stubs, mocks and spies out of the box. This post looks at how to instanti ...
#jest #node #javascript #testingJest Array/Object partial match with objectContaining and arrayContainingIt’s possible to do partial matches on Arrays and Objects in Jest using expect.objectContaining and expect.arrayContaining. expect has some powerful matcher methods to do things like the above partial matches. Using Jest at an advanced level means using tools like these to ...
#javascript #jest #node #testingJest explicitly or arbitrarily force fail() a testWhen testing code with Jest, it can sometimes be useful to fail a test arbitrarily. This post goes through a few scenarios where that might be useful and how to fail a Jest test explicitly/in a forced manner. It also presents more idiomatic Jest patterns that could be used interc ...
#javascript #jest #node #es6 #testingJest Full and Partial Mock/Spy of CommonJS and ES6 Module ImportsJavaScript import/require module testing do’s and don’ts with Jest The example repository is available at github.com/HugoDF/mock-spy-module-import. This post goes through how to achieve different types of module mocking scenarios with Jest. From simple Import interc ...
#jest #javascript #node #testingHow to run, ignore or skip Jest tests, suites and filesWhen debugging or writing units tests with Jest it can be useful to specify a single file or test to run or to exclude a specific failing test for the Jest run. This post goes how to skip and exclude a single test, a whole Jest test suite and a whole Jest test file using the CLI ...
#jest #javascript #node #testingHow to run Jest tests sequentiallyBy default Jest runs tests in parallel with a “a worker pool of child processes that run tests” (Jest CLI docs). As per the Jest documentation, running tests in sequence (serially), can be helpful for debugging purposes and for test run performance reasons. ...
#javascript #jest #testing #nodeJest ignore or exclude file/function/statement from test coverageIn computer science, test coverage is a measure used to describe the degree to which the source code of a program is executed when a particular test suite runs. Code coverage - Wikipedia Code coverage is usually used as a quality metric for software eg. “Our code has to have 80 ...
#javascript #jest #node #Testing #dateMocking/stubbing the current Date in Jest testsThere are situations where new Date() or Date.now is used in application code. That code needs to be tested, and it’s always a struggle to remember how to mock/stub or spy on Date.now/new Date with Jest. This post goes through multiple approaches to mocking, stubbing and spying o ...
#javascript #node #jest #testing #MongoDBAvoiding recursion pitfalls: MongoDB nested query clause addition and removalA case-study on where recursion can be useful for enterprise Node.js applications and how to avoid its common pitfalls like RangeError: Maximum call stack size exceeded. The full repository for this post is on GitHub: github.com/HugoDF/mongo-query-clause-modification We’ll ...
