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ViewsJest: function that should throw does not pass and test will fail
I want to test a function A that calls multiple other functions inside it which can throw errors.
Here is an abstraction of my code:
// file A.ts
const A = (args: any[]): boolean => {
(() => {
// nested function which throws
throw new RangeError("some arg not correct")
})()
return true
}
and
// file main.test.ts
test("should throw an error", () => {
expect(A()).toThrow()
})
How do I test this appropriately in Jest?
The test won't succeed and jest will log the thrown error.
Here is a sandbox and here is the output of the test you can see if you run test:
2 answers
Answer question0
I'm not good with typescript so I have written the examples using regular JS.
It turns out you do not need to call the A function to test if it throws:
// throw.test.js
const A = () => {
(() => {
// nested function which throws
throw new RangeError("some arg not correct")
})();
};
test("should throw an error", () => {
expect(A).toThrow();
})
which outputs
> jest
PASS ./throw.test.js
✓ should throw an error (6ms)
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 4.404s
Ran all test suites.
If you do want to call the function, say to pass an argument, call it within another function that's passed to the expect:
// throw2.test.js
const A = () => {
(() => {
// nested function which throws
throw new RangeError("some arg not correct")
})();
};
test("should throw an error", () => {
expect(() => A('my-arg')).toThrow();
})
0
I refactored a function that was async to no longer be async and was getting this error. So, if you have an inner-async function, use this approach:
test("async function throws", async() => {
await expect(() => A('my-arg')).rejects.toThrow();
})
You can also do some more specific checks like, what kind of error and the message, etc.
test("async function throws", async() => {
await expect(() => A('my-arg')).rejects.toThrow(MyError("Specific Error Message");
})