style: Document location of `TestMain()` function

While many tests use a `testhelper_test.go` file to implement
`TestMain()`, this is not common to all. This makes test setup harder to
find than necessary. This commit thus documents the recommended name of
"testhelper_test.go" for such code.

1 files changed, 5 insertions, 0 deletions

diff --git a/STYLE.md b/STYLE.md
index 8230c8f9d..2461867a0 100644
--- a/STYLE.md
+++ b/STYLE.md
@@ -247,6 +247,11 @@ practices](https://prometheus.io/docs/practices/naming/) and be aware of
 the
 [gotchas](https://prometheus.io/docs/practices/instrumentation/#things-to-watch-out-for).
 
+### Main function
+
+If tests require a `TestMain()` function for common setup, this function should
+be implemented in a file called `testhelper_test.go`
+
 ## Git Commands
 
 Gitaly relies heavily on spawning git subprocesses to perform work. Any git