I want my tests to fail whenever there an error logged, and I do not want to repeat an expect clause for that in every test.
I stubbed my logger.error function, thinking I could just fail from within the stub.
Neither calling assert.fail nor throwing an Error causes the test to fail:
loggerErrorStub = sinon.stub(Logger.prototype, 'error').callsFake((msg) => {
console.log(`[[ERROR]] MSG: ${msg}`);
assert.fail(`actual`, `expected`, `message`);
throw new Error();
});
Calling either of these in the body of the describe/it clause works fine. So, I'm guessing the problem is, within the stub, Mocha is missing some context.
I could always add an expect clause at the end of the it such as expect(loggerErrorStub).to.not.have.been.called, but I want this to happen with ALL my tests, and do not want to repeat that line in every test.
I know I could throw an error from inside the test, but I wonder if there is something like the global fail() method provided by Jasmine?
Jest actually uses Jasmine, so you can use fail just like before.
Sample call:
fail('it should not reach here');
Here's the definition from the TypeScript declaration file for Jest:
declare function fail(error?: any): never;
If you know a particular call should fail you can use expect.
expect(() => functionExpectedToThrow(param1)).toThrow();
// or to test a specific error use
expect(() => functionExpectedToThrow(param1)).toThrowError();
See Jest docs for details on passing in a string, regex, or an Error object to test the expected error in the toThrowError method.
For an async call use .rejects
// returning the call
return expect(asyncFunctionExpectedToThrow(param1))
.rejects();
// or to specify the error message
// .rejects.toEqual('error message');
With async/await you need to mark the test function with async
it('should fail when calling functionX', async () => {
await expect(asyncFunctionExpectedToThrow(param1))
.rejects();
// or to specify the error message
// .rejects.toEqual('error message');
}
See documentation on .rejects and in the tutorial.
Also please note that the Jasmine fail function may be removed in a future version of Jest, see Yohan Dahmani's comment. You may start using the expect method above or do a find and replace fail with throw new Error('it should not reach here'); as mentioned in other answers. If you prefer the conciseness and readability of fail you could always create your own function if the Jasmine one gets removed from Jest.
function fail(message) {
throw new Error(message);
}
You can do it by throwing an error. For example:
test('Obi-Wan Kenobi', () => {
throw new Error('I have failed you, Anakin')
})
Copy/pasta failing test:
it('This test will fail', done => {
done.fail(new Error('This is the error'))
})
Here are certain scenarios where some of the answers won't work. In a world of async-await, it is quite common to have try-catch logic like so.
try {
await someOperation();
} catch (error) {
expect(error.message).toBe('something');
}
Now imagine if someOperation() somehow passed, but you were expecting it to fail, then this test will still pass because it never went to the catch block. So what we want is to make sure that the test fails if someOperation does not throw an error.
So now let's see which solutions will work and which won't.
Accepted answer won't work here because the throw will be catched again.
try {
await someOperation();
throw new Error('I have failed you, Anakin');
} catch (error) {
console.log('It came here, and so will pass!');
}
The answer with true === false also won't work because, assertions too throw an error like above which will be catched.
try {
await someOperation();
expect(true).toBe(false); // This throws an error which will be catched.
} catch (error) {
console.log('It came here, and so will pass!');
}
The one solution that DOES WORK (as shown in #WhatWouldBeCool's answer) for this case is below. Now it explicitly fails the test.
try {
await someOperation();
fail('It should not have come here!')
} catch (error) {
console.log('It never came here!');
}
Update May-2022
The fail() function is not officially supported by Jest anymore. Instead, you can do a couple of things to fail explicitly.
Method-1
You can wrap your promise function within expect and tell jest the function should reject with the given error. If the someOperation() somehow passes, jest will throw an error. If the someOperation() fails for any other reason other than the one you specified, it will throw an error. There are also different methods other than toThrowError() that you can use.
await expect(someOperation()).rejects.toThrowError('error!')
Method-2
You can declare explicitly how many assertions you expect in your test. If that doesn't match because someOperation() never failed, jest would throw an error.
expect.assertions(1)
try {
await someOperation();
} catch (error) {
expect(error.message).toBe('something');
}
Dont think there is, discussed here: https://github.com/facebook/jest/issues/2129
A lot of good ideas here. Only to add extra info about testing async code which may lead to trying to make Jest explicitly fail, check the docs for Testing Asynchronous Code https://jestjs.io/docs/en/asynchronous
To test a function that returns a Promise that resolves, it's important to return the Promise, so Jest knows that the test is done only when the Promise is resolved or it'll time out:
test('the data is peanut butter', () => {
return fetchData().then(data => {
expect(data).toBe('peanut butter')
})
})
To test a function that returns a Promise that rejects, it's important to return the Promise, so Jest knows that the test is done only when the Promise is rejected or it'll time out. And also have to say how many assertions Jest needs to count or it won't fail if the Promise is resolved - which is wrong in this case -:
test('the fetch fails with an error', () => {
expect.assertions(1)
return fetchData().catch(e => expect(e).toMatch('some specific error'))
})
You can always do something like this :)
expect(true).toBe(false);
The done callback passed to every test will throw an error if you pass a string to it.
for instance
it('should error if the promise fails', async (done) => {
try {
const result = await randomFunction();
expect(result).toBe(true);
done();
} catch (e) {
done('it should not be able to get here');
}
});
In this following code if the randomFunction throws an error it will be caught in the catch and with auto fail due to the string being passed to done.
Add jest-fail-on-console npm package, then on your jest.config.js
import failOnConsole from 'jest-fail-on-console'
failOnConsole();
This will fail a test once there is a console error or warning done by jest because of an error or warning thrown in the test item.
I just ran into this one, and after some digging, I found the root of the issue.
Jest, since its inception, has been compatible with Jasmine. Jasmine provided a fail function for programmatically fail the test. This is very useful for cases where throwing an error would cause the test to pass incorrectly (overly-simplified example, but hopefully illustrates the use-case):
function alwaysThrows() {
throw new Error();
}
describe('alwaysThrows', () => {
it('should throw', () => {
try {
alwaysThrows();
// here if there is nothing to force a failure, your
// test could "pass" as there are no failed expectations
// even though no error was thrown. If you just put the
// following to prevent that, you actually force the test
// to always pass:
throw new Error('it should have failed');
// that's why instead you use Jasmine's `fail(reason)` function:
fail('it should have failed');
} catch(err) {
expect(err).toBeDefined();
}
});
)
});
So, what has happened is this:
originally Jest did have a fail() function defined, because its default test runner was jest-jasmine2, which provided fail().
In Jest version 27 (or thereabouts), Jest replaced jest-jasmine2 with jest-circus as the default test runner. jest-circus does not implement a fail() function. This was reported as a bug on July 28th 2021: https://github.com/facebook/jest/issues/11698
Jest's type definitions (maintained in DefinitelyTyped) did not remove the fail() function, so autocompletion and the TypeScript compiler still think that it exists and can be used. There is an issue going on in DefinitelyTyped as well: https://github.com/DefinitelyTyped/DefinitelyTyped/discussions/55803
The issue with this thread is that they have decided not to remove it from the type definitions as it is marked as a "regression" in the Jest repository. Unfortunately, the Jest repository's thread has no official response about whether or not they will support this in the future, so the type definitions are in limbo.
So, long story short, Jest doesn't support fail() by default, but knowing that it's a matter of the default task runner, you can restore the fail() functionality by telling Jest to use the jest-jasmine2 runner instead of the default jest-circus runner:
npm i -D jest-jasmine2
configure the Jest config:
module.exports = {
testRunner: "jest-jasmine2"
};
P.S.: usually there is a better way than try/catch to account for errors in your actual test cases. You can see an example of different ways to handle errors without requiring try/catch in both synchronous and asynchronous contexts here: https://gist.github.com/joeskeen/d9c053b947e5e7462e8d978286311e83
You can throw an error simulating an error thrown by the application and then expect its message to be different from what it actually is.
try {
await somthingYouExpectToFail();
throw new Error("Fail!");
} catch (error) {
expect(error.message).not.toBe("Fail!");
}
1) Can anyone explain why, when debugging this jasmine test for hapi, the debugger never hits any breakpoint inside the injected section (see comment) unless done is called later on? How can the absence of a line of code that is not yet reached affect the debugger earlier on ?
I am aware that it is important to call the done method (which I have commented out on purpose). I am however surprised by the consequences.
2) Another unfortunate side-effect of forgetting to call the done method is that the test always passes. Instead of passing I would rather see it fail if I make an error. Any suggestions?
const server = require("../lib/server");
describe("Server hello", function () {
it("returns status code 200", function (done) {
server.inject({ method: 'GET', url: '/' }, (res) => {
// Never reached if done uncommented - even by debugger breakpoint - why?");
console.log("GOT " + res.payload);
expect(res.statusCode).toBe(200);
// done(); // Test always passes if uncommented - is there any way to force an error instead?
});
});
});
Read the source, Luke! Jasmine docs for asynchronous testing note:
This spec will not start until the done function is called in the call to beforeEach above. And this spec will not complete until its done is called.
So if you don't call done your suite is not run, not that it runs and times out!
I am currently attempting to test Flux with Sinon + Sinon-As-Promised, but I am struggling to find relevant examples, and having an issue with my test always returning true, no matter the assertion.
My test currently looks like this:
it('Form store should contain encounter object', function() {
var stub = sinon.stub(restService, "loadForm").resolves(mockDataEncounter.Encounter);
stub().then(function(value){
console.log('Inside frmSrv');
formStore._currentForm = value;
expect(formStore._currentForm).to.have.property('Name');
})
console.log('calling action creator');
actionCreator.loadForm("123456789012345678910003");
})
What I was expecting to happen was -
Call action creator -> Action creator usually makes the API call,
but in this case calls the stubbed method instead -> Promise is
resolved, _currentForm is set to the mock data, and then the assertion
is checked.
However what actually happens is:
Call action creator -> Test passes -> Promise resolves
If I add a done callback to the test, and then call done after the assertion, this causes things to execute in my expected order, but then if I modify the expected property to "Name1"(which doesnt exist), the test fails with a timeout error rather than the correct error to say the property doesnt exist.
Am I missing something fundamental here, or just going about things completely the wrong way?
So after some more fiddling I worked it out, I had to add a catch to the promise, and then call done passing in the error in order to get the correct failure message to display.
it('Form store should contain encounter object', function(done) {
var stub = sinon.stub(restService, "loadForm").resolves(mockDataEncounter.Encounter);
stub().then(function(value){
console.log('Inside frmSrv');
formStore._currentForm = value;
expect(formStore._currentForm).to.have.property('Name');
done();
}).catch(function(err){
done(err);
});
console.log('calling action creator');
actionCreator.loadForm("123456789012345678910003");
})
I am trying to understand how the asynchronous code for Mocha (at http://mochajs.org/#getting-started) works.
describe('User', function() {
describe('#save()', function() {
it('should save without error', function(done) {
var user = new User('Luna');
user.save(function(err) {
if (err) throw err;
done();
});
});
});
});
I want to know how Mocha decides whether a test has succeeded or failed behind the scenes.
I can understand from the above code that user.save() being asynchronous would return immediately. So Mocha would not decide if the test has succeeded or failed after it executes it(). When user.save() ends up calling done() successfully, that's when Mocha would consider it to be a successful test.
I cannot understand how it Mocha would ever come to know about a test failure in the above case. Say, user.save() calls its callback with the err argument set, then the callback throws an error. None of Mocha's function was called in this case. Then how would Mocha know that an error occurred in the callback?
Mocha is able to detect failures that prevent calling the callback or returning a promise because it uses process.on('uncaughtException', ...); to detect exceptions which are not caught. Since it runs all tests serially, it always knows to which test an uncaught exception belongs. (Sometimes people are confused by this: telling Mocha a test is asynchronous does not mean Mocha will run it in parallel with other tests. It just tells Mocha it should wait for a callback or a promise.)
Unless there is something that intervenes to swallow exceptions, Mocha will know that the test failed and will report the error as soon as it detects it. Here is an illustration. The first test fails due to a generic exception thrown. The 2nd one fails due to an expect check that failed. It also raises an unhandled exception.
var chai = require("chai");
var expect = chai.expect;
it("failing test", function (done) {
setTimeout(function () {
throw new Error("pow!");
done();
}, 1000);
});
it("failing expect", function (done) {
setTimeout(function () {
expect(1).to.equal(2);
done();
}, 1000);
});
This is the output on my console:
1) failing test
2) failing expect
0 passing (2s)
2 failing
1) failing test:
Uncaught Error: pow!
at null._onTimeout (test.js:6:15)
2) failing expect:
Uncaught AssertionError: expected 1 to equal 2
+ expected - actual
-1
+2
at null._onTimeout (test.js:13:22)
The stack traces point to the correct code lines. If the exceptions happened deeper, the stack would be fuller.
When Mocha cannot report what went wrong exactly, that's usually because there is intervening code that swallows the exception that was raised. Or when you use promises the problem may be that someone forgot to call a method that indicates whether the promise is supposed to be completely processed and unhandled exceptions should be thrown. (How you do this depends on the promise implementation you use.)
It won't, it's a shame. It has no way to know that your callback is executing. It's an easier way to do asynchronous testing, where you just tell the test when you are finished. The downside, as you have noticed, is that errors in asynchronous callbacks won't be detected. Nevermind, Mocha hooks to process.on('uncaughtException',...) as mentioned by Louis. Note that if you use done instead of waitsFor and runs in jasmine, then you will have the problem.
Other frameworks like js-test-driver force to you wrap callbacks so the the testing framework can put a try catch around your callbacks (and you don't need to call done). Your test would look like the following:
var AsynchronousTest = AsyncTestCase('User');
AsynchronousTest.prototype.testSave = function(queue) {
queue.call('Saving user', function(callbacks) {
var user = new User('Luna');
user.save(callbacks.add(function(err) {
if (err) throw err;
// Run some asserts
}));
});
};