How to test the type of a thrown exception in Jest

In Jest you have to pass a function into expect(function).toThrow(<blank or type of error>).

Example:

test("Test description", () => {  const t = () => {    throw new TypeError();  };  expect(t).toThrow(TypeError);});

Or if you also want to check for error message:

test("Test description", () => {  const t = () => {    throw new TypeError("UNKNOWN ERROR");  };  expect(t).toThrow(TypeError);  expect(t).toThrow("UNKNOWN ERROR");});

If you need to test an existing function whether it throws with a set of arguments, you have to wrap it inside an anonymous function in expect().

Example:

test("Test description", () => {  expect(() => {http.get(yourUrl, yourCallbackFn)}).toThrow(TypeError);});

It is a little bit weird, but it works and IMHO is good readable:

it('should throw Error with message \'UNKNOWN ERROR\' when no parameters were passed', () => {  try {      throwError();      // Fail test if above expression doesn't throw anything.      expect(true).toBe(false);  } catch (e) {      expect(e.message).toBe("UNKNOWN ERROR");  }});

The Catch block catches your exception, and then you can test on your raised Error. Strange expect(true).toBe(false); is needed to fail your test if the expected Error will be not thrown. Otherwise, this line is never reachable (Error should be raised before them).

@Kenny Body suggested a better solution which improve a code quality if you use expect.assertions():

it('should throw Error with message \'UNKNOWN ERROR\' when no parameters were passed', () => {  expect.assertions(1);  try {      throwError();  } catch (e) {      expect(e.message).toBe("UNKNOWN ERROR");  }});

See the original answer with more explanations: How to test the type of a thrown exception in Jest

I use a slightly more concise version:

expect(() => {  // Code block that should throw error}).toThrow(TypeError) // Or .toThrow('expectedErrorMessage')