Sinon stub with a return value

sinon-stub-return.ts

attempt_CallsOnFail_IfMyApiFails() {
    // Arrange
    const onFail = sinon.stub();
    const onSucceed = sinon.stub();
    const externalApi = sinon.stub().returns(false);
    const actor = new Actor({ externalApi, onFail, onSucceed });

    // Act
    actor.attempt(); // internally calls externalApi

    // Assert
    UTF.Assert.True("onFail should have been called", onFail.calledOnce);
}