You need to add the test setup statement.
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From Django documentation:
Although * your code * [+] would work in the Python interactive interpreter, some of the test client’s functionality, notably the template-related functionality, is only available while tests are running. The reason for this is that Django’s test runner performs a bit of black magic in order to determine which template was loaded by a given view. This black magic (essentially a patching of Django’s template system in memory) only happens during test running.
So if you run it in a test run, it should work.
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