download_fixtures function does not check for the fixtures version

[gurukamath]

See download_fixtures

Currently, the testing framework downloads the json fixtures as and when needed. There are two methods for this - 1. using git clone 2. download raw fixtures (using the download_fixtures function)

While the former checks out the appropriate version of the fixtures, the latter does not. The download_fixtures only checks if the fixtures folder is available. This could lead to issues if the fixture version has been changed or the downloaded fixtures have been corrupted in some way.

At the same time, it might not be optimal to download the fixtures everytime, even when the correct fixtures are already present from a previous run. Some middle ground has to be worked out here.