testhelper: Unify setup of test suites

Setup of a test package's main function is quite repetitive: we call a
separate `testMain()` function such that we can use `defer` calls, this
function calls `MustHaveNoChildProcess()` and `Configure()`, and then we
return the result of `m.Run()`. This is almost always exactly the same,
with some exceptions where we need to have additional setup code.

Unify this code via a single `testhelper.Run()` function which does all
of this. It allows us greater flexibility in the setup code such that we
can easily perform additional validation after the tests without having
to modify all callsites.

Note that this change removes calls to the goleak package in some
places. These will resurface in a later commit in this patch series,
where we instead move this call into `testhelper.Run()` such that it is
executed by default.

1 files changed, 4 insertions, 16 deletions

diff --git a/STYLE.md b/STYLE.md
index a67515d6a..e663c397a 100644
--- a/STYLE.md
+++ b/STYLE.md
@@ -238,22 +238,10 @@ importantly, this includes any calls to `log.Fatal()` and related functions.
 
 ### Common setup
 
-When all tests require a common setup, we use the `TestMain()` function for
-this. `TestMain()` must call `os.Exit()` to indicate whether any tests failed.
-As this will cause deferred function calls to not be processed, we use the
-following pattern:
-
-```
-func TestMain(m *testing.M) {
-	os.Exit(testMain(m))
-}
-
-func testMain(m *testing.M) int {
-	cleanup := testhelper.Configure()
-	defer cleanup()
-	return m.Run()
-}
-```
+The `TestMain()` function shouldn't do any package-specific setup. Instead, all
+tests are supposed to set up required state as part of the tests themselves. All
+`TestMain()` functions must call `testhelper.Run()` though, which performs the
+setup of global state required for tests.
 
 ## Black box and white box testing