t.throws RegExp not matching correctly

[Jameskmonger]

I have two tests:

test('this should pass', t => {
    t.plan(1);

    t.throws(() => {
        throw new Error('This is my error message.This text here should still match.')
    }, /This is my error message./);
});

test('this should fail', t => {
    t.plan(1);

    t.throws(() => {
        throw new Error('This is my error message.This text here should now fail.');
    }, /^This is my error message.$/);
});

The first test passes, as expected, because I don't specify the start and end of the RegExp matcher using ^ and $. The second, however, should no longer match the whole error message and should fail. These two behave as expected.

When I add a third test, however:

test('this should however pass', t => {
    t.plan(1);

    t.throws(() => {
        throw new Error('This is my error message.');
    }, /^This is my error message.$/);
});

I expect this to pass, because the whole string matches the RegExp. The test fails with the following output:

# this should however pass
not ok 8 should throw
  ---
    operator: throws
    expected: |-
      '/^This is my error message.$/'
    actual: |-
      { [Error: This is my error message.] message: 'This is my error message.' }
    at: Test.<anonymous> (/home/james/Development/jenie/test/jenie/jenie.spec.js:67:7)
  ...

[ljharb]

@Jameskmonger This works with the $ anchor - but the reason it's not working with the ^ anchor is that with an Error object, the message isn't what's being tested - but rather, the string version of the Error instance itself - which includes the type.

so, in your case, it would be /^Error: This is my error message.$/ that passes.

[ljharb]

I've added some tests that demonstrate this, and will close the issue.

[ljharb]

(also, dupe of #182)

[Jameskmonger]

Thanks @ljharb

[jtlapp]

This behavior really should be in the documentation so everyone isn't having to rediscover it. Right now all it says is "expected, if present, must be a RegExp or Function."