MockPropertyContext.mockImplementationOnce method | Node.js node:test module | Bun

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);
});

The value to be used as the mock's implementation for the invocation number specified by onAccess.

The invocation number that will use value. If the specified invocation has already occurred then an exception is thrown. Default: The number of the next invocation.