API docs: missing test coverage

[emidoots]

As I work on API docs, it's more important that we get an MVP out and be iterative than it is to have excellent test coverage.

I will not introduce changes that could affect other parts of Sourcegraph negatively without appropriate test coverage.

It also does not mean that we do not want excellent test coverage eventually. This issue exists to track what improvements can be made and where, to ensure I can accurately revisit this topic later on in the project (6-ish months from now)

• lsif/protocol/reader unmarshalling tests
• Everything in the LSIF backend (ingestion/conversion, DB schema, etc.) and https://github.com/sourcegraph/sourcegraph/pull/21223
• Unit tests for lsif-go implementation
• Web UI