React\Promise\FunctionReduceTest::shouldReduceValuesWithoutInitialValue PHP Method

    public function shouldReduceValuesWithoutInitialValue()
    {
        $mock = $this->createCallableMock();
        $mock->expects($this->once())->method('__invoke')->with($this->identicalTo(6));
        reduce([1, 2, 3], $this->plus())->then($mock);
    }