Hspec support request

[peterbecich]

Describe the feature request
I have a feature request in Hspec to make it easier to run specific tests with Cabal: hspec/hspec#862

Hspec needs to know if it is run by Cabal.

@sol suggests this can be implemented if cabal test sets the environment variable CABAL_TEST_COMMAND=cabal

Additional context

Currently a failing test will print:

To rerun use: --match "/someFailingTest/"

To use this suggestion with Cabal, it must be modified to this:

cabal test --test-options="--match \"/someFailingTest/\""

With this environment variable, Hspec will print out this feedback for Cabal.

[Bodigrim]

Why could not hspec determine its parent process? E. g., https://hackage.haskell.org/package/unix-2.8.3.0/docs/System-Posix-Process-ByteString.html#v:getParentProcessID.

[geekosaur]

Finding its ppid is POSIX-portable; finding out anything about its parent isn't (/proc doesn't always exist and when it does isn't necessarily Linux-compatible).

[geekosaur]

Also note that Windows is a wildcard here.

[Bodigrim]

True, and nevertheless pretty much every OS provides means to determine a parent process. We might lack a crossplatform Haskell library to do this reliably, in which case it would be better to write one instead of establishing an ad-hoc communication channel between cabal and hspec. (But I've been just passing by, nevermind)

[gbaz]

note that running a testsuite already does affect the environment, in that it ensures datadir is set. Testing for this is slightly ad-hoc as opposed to a distinguished variable, but it has the great advantage of already existing and working!

cabal/Cabal/src/Distribution/Simple/Test/ExeV10.hs

Line 87 in 9f37325

pkgPathEnv =

[andreabedini]

@peterbecich a totally under-engineered option is to expand the message to the user:

To rerun use: --match "/someFailingTest/".
If you are using cabal use: cabal test --test-options="--match \"/someFailingTest/\""

(maybe --test-options='--match "/someFailingTest/"' would also work?)