fn

fun <F : Function<*>> fn(original: F = definedExternally, options: MockFunctionOptions = definedExternally): Mock<F>(source)

This function is used to create a mock function.

The following example creates a mock function that increments a counter by one on each invocation. The times option is used to modify the mock behavior such that the first two invocations add two to the counter instead of one.

test('mocks a counting function', (t) => {
  let cnt = 0;

  function addOne() {
    cnt++;
    return cnt;
  }

  function addTwo() {
    cnt += 2;
    return cnt;
  }

  const fn = t.mock.fn(addOne, addTwo, { times: 2 });

  assert.strictEqual(fn(), 2);
  assert.strictEqual(fn(), 4);
  assert.strictEqual(fn(), 5);
  assert.strictEqual(fn(), 6);
});

Since

v19.1.0, v18.13.0

Return

The mocked function. The mocked function contains a special mock property, which is an instance of {@link MockFunctionContext}, and can be used for inspecting and changing the behavior of the mocked function.

Parameters

original

An optional function to create a mock on.

implementation

An optional function used as the mock implementation for original. This is useful for creating mocks that exhibit one behavior for a specified number of calls and then restore the behavior of original.

options

Optional configuration options for the mock function.

fun <F : Function<*>> fn(original: F = definedExternally, implementation: Function<*> = definedExternally, options: MockFunctionOptions = definedExternally): Mock<Function<*>>(source)