Added music composition mutations and tests

[alastair]

This PR can delete work.py too, if this code is duplicated

[pc2752]

I'm not sure why the conflicts are not showing up on my end again, but I've made the changes required.

[pc2752]

git fetch origin and git pull just show "Already up-to-date", with no conflicts. But this page shows conflicts in 5 files.

[alastair]

what branch are you on when you're running those commands? your add_composition one? You'll have to merge master into the branch to fix these conflicts. Try this:

git checkout master
git fetch origin
git merge origin/master
git checkout add_composition
git merge master

[alastair]

great, thanks. Will get this merged today

[alastair]

I've made some changes to this, please take a look at them:

• Remove work.py and test_composition.py, these were unneeded now that we have the musiccomposition version
• I updated the structure of mutation_update_music_composition to not duplicate as much code

Can you please look at the tests for musiccomposition and update the following things:

• Make the test files look more "correct" - e.g. EXPECTED_MUSICCOMPOSITION.txt seems to have field values that look more like a Document or a Person. These should at least look like an example from our modelling doc
• rename the expected text files to lower-case, and a better name structure, like I did with person
• Add some tests for create_musiccomposition and update_musiccomposition to test that exceptions are raised with bad data (e.g an invalid language or a format without a / in it)
• add tests to check that optional values are not added if they're not given - e.g. do 2 tests for update_musiccomposition - one with only the required fields, check that only those fields are listed in the mutation, and one with all fields set, and make sure that all those fields are written in the mutation text.

thanks!

[alastair]

Looks good, but I see 3 failing tests:

looks like they're all to do with loading the expected text file