to have arity

  • <function> to have arity <number>

Asserts that the function takes the given number of arguments.

expect(Math.max, 'to have arity', 2);
expect('wat'.substring, 'to have arity', 2);

In case of a failing expectation you get the following output:

expect(function wat(foo, bar) {
  return foo + bar;
}, 'to have arity', 3);
expected function wat(foo, bar) { return foo + bar; } to have arity 3