mockImplementationOnce

This function is used to change the behavior of an existing mock for a single invocation. Once invocation onAccess has occurred, the mock will revert to whatever behavior it would have used had mockImplementationOnce() not been called.

The following example creates a mock function using t.mock.property(), calls the mock property, changes the mock implementation to a different value for the next invocation, and then resumes its previous behavior.

test('changes a mock behavior once', (t) => {
  const obj = { foo: 1 };

  const prop = t.mock.property(obj, 'foo', 5);

  assert.strictEqual(obj.foo, 5);
  prop.mock.mockImplementationOnce(25);
  assert.strictEqual(obj.foo, 25);
  assert.strictEqual(obj.foo, 5);
});

Parameters