With a directory layout (not so uncommon):

tests/Doctest.hs
tests/Spec.hs
tests/Spec/FooSpec.hs

and package.yaml

tests:
  spec:
    main:            Spec.hs
    source-dirs:     test
  doctest:
    main:            Doctest.hs
    source-dirs:     test

the following pkg.cabal is generated (only relevant parts):

test-suite doctest
  type: exitcode-stdio-1.0
  main-is: Doctest.hs
  hs-source-dirs:
      test
  other-modules:
      Spec
      Spec.FooSpec

test-suite spec
  type: exitcode-stdio-1.0
  main-is: Spec.hs
  hs-source-dirs:
      test
  other-modules:
      Doctest
      Spec.FooSpec

This haven't been a problem so-far as other-modules weren't yet passed to GHC by cabal-install for tests and benchmarks.
Newest cabal will however pass them, which will cause GHC to fail with

test/Doctest.hs:1:8: error:
    File name does not match module name:
    Saw: ‘Main’
    Expected: ‘Doctest’
  |
1 | module Main (main) where

The reason to pass other-modules is for GHC to avoid interleaving module
discovery (cabal-file already tells which modules to compile!) and compilation in GHC.

Even proper solution would be to have a way to turn off/configure module discovery per executable/test-suite/benchmark, in addition to filtering out main-is files.