Increase test coverage

[wolfgangwalther]

To be able to properly use coverage overlays (#1713), we need to increase coverage close to 100%. Many of the files are close to that already.

This issue is to track progress across PRs.

TODO:

• Main
  • Add tests for schema reload on notify (see Missing tests - recovery tests #1766)
  • Add tests dealing with database connection problems (see Missing tests - recovery tests #1766)
• UnixSocket
  • Add test to throw when unix socket already exists
• PostgREST.ApiRequest
  • Add test with empty query param (?key=) (line 171)
  • Add test with + in query string converted to space (line 183)
  • Debug "application/x-www-form-urlencoded" (line 215)
  • Add test for POST with unsupported Content-Type body (line 240)
  • Add test for unsupported request method (line 259)
• PostgREST.App
  • Make any RPC STABLE (line 112) (should we test for read only transaction somehow?) (Refactor dbStructure.hs #1720)
  • Add tests that throw with POST, PATCH, DELETE (lines 160, 195, 254)
  • Check whether count queries can actually throw (lines 138, 170, 204, 237, 264)
  • Add test to return count on PATCH (line 212)
  • Add OPTIONS request to missing endpoint (line 285)
  • Check whether pdName can be covered in line 292
  • Find out why tablePKCols dbStructure s tn is not covered in line 329
• PostgREST.Auth
  • Add roleclaimkey tests that try to access objects with arrays presents or vice-versa (line 89)
  • Check whether constructing a JWT with something different from an object as top-level json value can be constructed (line 82)
  • Add test with empty jwt-aud (line 64)
• PostgREST.Config (Add basic io tests and remove unused code #1717)
  • Add tests for error messages on config errors
• PostgREST.DbRequestBuilder
  • Understand whats happening here...
• PostgREST.DbStructure (Refactor dbStructure.hs #1720)
  • Refactor addHasVariadic to in-SQL (line 145)
  • Refactor parseArg to in-SQL to solve TODO and coverage (line 161)
  • Add schema description to fixtures (line 247)
  • Refactor combinations to allow better Pattern Matching in line 404
  • Refactor addViewM2ORels to remove Pattern Matching in line 342
• PostgREST.Error
• PostgREST.Middleware (Refactor Middleware.hs #1724)
  • Refactoring
  • Add logging tests
• PostgREST.OpenAPI
• PostgREST.Parsers
• PostgREST.Private.Common
• PostgREST.Private.ProxyUri
• PostgREST.Private.QueryFragment
• PostgREST.QueryBuilder
• PostgREST.RangeQuery
• PostgREST.Statements
• PostgREST.Types

[steve-chavez]

Noted that we only run coverage on pg 15. This generates some drop for code paths that only run on pg 9.6 and lower, like: https://github.com/PostgREST/postgrest/pull/2843/files#r1248317325

[steve-chavez]

Show instances added on #2847 dropped the coverage a bit. Related to this need #2627.

Ideally we'd be able to use our doctests to cover those. An alternative could be moving the doctests to unit tests.