@rbxts/expect > err

err() function

Helper function for testing expect error messages.

Throws an error if the callback doesn't throw.

Signature:

declare function err(callback: () => unknown, ...messages: string[]): void;

Parameters

Parameter	Type	Description
callback	() => unknown	The function to wrap around.
messages	string[]	A variable amount of substrings to look for in the message.

Returns:

void

Remarks

Intended to be used in test (.spec.ts) files.

Used internally for testing and other error messages, so that internal issues don't cause tests to accidentally pass.

Example 1

Testing for errors:

err(() => {
  expect([1]).to.be.empty();
});

Output:

The function did not throw a message.

Example 2

Testing for certain errors:

err(() => {
  expect([1]).to.be.empty();
}, `Expected '[1]' to be empty, but it had an element`);

Output if the string(s) weren't found in the error:

The function threw with the wrong message.

  Expected Message:
  Expected '[1]' to be empty, but it had an element

  Actual Message:
  Expected '[1]' to be empty, but it had the element '1'

Output if the function didn't throw at all:

The function did not throw a message.

  Expected Messages:
  Expected '[1]' to be empty, but it had an element

Example 3

Testing for multiple substrings:

err(() => {
  expect([1]).to.be.empty();
}, "to be empty", "but it had an element");

If it doesn't find any of the provided substrings, it will throw with that specific substring:

The function threw with the wrong message.

  Expected Message:
  "but it had an element"

  Actual Message:
  Expected '[1]' to be empty, but it had the element '1'