Symfony PHPUnit mocking: Error: Call to undefined method PHPUnit_Framework_MockObject_Builder_InvocationMocker::someMethod

My code:

public function testApiClient()
{
    $mock = createMockApiClient();
    dump($mock->someMethod());
}

protected function createMockApiClient()
{

    $mockApiClient = $this->createMock(ApiClient::class);
    return $mockApiClient
        ->expects($this->any())
        ->method('someMethod')
        ->will($this->returnValue('someString'))
    ;
}

So I have this error:

Error: Call to undefined method 
PHPUnit_Framework_MockObject_Builder_InvocationMocker::someMethod()

I'm new in PHPUnit tests, so what to do? I can't understand why I do as wrote in example and no result - just error?