Symfony Testing - ClockMock / DateTime
The ClockMock doesn't work for new \DateTime() but only on time-based PHP function.
From the announcement of the features:
This means that you don't need to make a single change in your original code, except when using
new DateTime(), which must be replaced byDateTime::createFromFormat('U', time())to use the mockedtime()function.
So try as suggested: replace any DateTime object creation with the named-constructor with the time function.
Hope this help