Start writing tests and stuff

Closes #3475410

added 3 commits

• 177e709a - 1 commit from branch project:3.0.x
• c213735d - Fill in schema
• a8f20206 - Merge branch '3.0.x' into 3475410-convert-storage-backends

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added 1 commit

• ff8be657 - Adapt plugin implementations to Task content entity

Compare with previous version

added 3 commits

• ff8be657...1cf3afa7 - 2 commits from branch project:3.0.x
• 2a383add - Merge branch '3.0.x' into 3475410-convert-storage-backends

Compare with previous version