Improve maintainability of dotnet tests

[laingsimon]

Some test fixtures are very long, due to complex setup; review if these can be simplified to reduce difficulties in maintaining the codebase.

• Introduce helpers/builders?
• Split up test fixtures into sub-fixtures

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Fixtures with 500+ lines:

File	Lines
UpdateScoresCommandTests.cs	641

[laingsimon]

 get-childitem -recurse | where-object { $_.Name.EndsWith(".cs") -and $_.FullName.Contains("Tests") } | select-object @{ label='name'; expression={$_.name} }, @{ label='lines'; expression={(Get-Content $_.FullName | Measure-Object -Line).Lines} } | where-object { $_.lines -gt 500 } | sort-object -descending -property 'lines' | select-object { "| $($_.name) | $($_.lines) |" }