Tests and updates added for data/load.py

[JMP-MO]

Added a tests file for the data.load.py file.

During testing I found the original file doesn't raise errors when passing incorrect data types so I added an error check for this.
I also added comments to the original code file as these helped me test its functionality and understand the purpose of the code and I thought they would be useful for others. I also reformated the list indexing syntax to be more conventional.

All tests were passing and I tested by running some of the tutorial notebooks to check for changes in behaviour.

[coveralls]

Pull Request Test Coverage Report for Build 14513344028

Details

• 43 of 43 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 58.806%

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Totals
Change from base Build 14513314052:	0.2%
Covered Lines:	7919
Relevant Lines:	13098

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💛 - Coveralls

[tennlee]

Looks great! pre-commit is still complaining a little. I'll tidy it up post-merge, but we should catch up next week and check why there's an inconsistency.