example\EitherMonadTest::test_it_should_concat_content_of_two_files_only_when_files_exists PHP Method

    public function test_it_should_concat_content_of_two_files_only_when_files_exists()
    {
        $concatF = f\liftM2(function ($first, $second) {
            return $first . $second;
        });
        $concat = $concatF(read(__FILE__), read('aaa'));
        $this->assertInstanceOf(Either\Left::class, $concat);
        $this->assertEquals(e\left('File "aaa" does not exists'), $concat);
    }