pw_build: Detect test.cc as a test file

Change-Id: I77de3edb6ee5a46b476771584f16c669d6ba40ba
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/45340
Pigweed-Auto-Submit: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Vic Yang <victoryang@google.com>

pw_build/pigweed.cmake

diff --git a/pw_build/pigweed.cmake b/pw_build/pigweed.cmake
index 37b0212..9a2c617 100644
--- a/pw_build/pigweed.cmake
+++ b/pw_build/pigweed.cmake
@@ -69,7 +69,8 @@
 
   # Create a library with all source files not ending in _test.
   set(sources "${all_sources}")
-  list(FILTER sources EXCLUDE REGEX "_test(\\.cc|(_c)?\\.c)$")
+  list(FILTER sources EXCLUDE REGEX "_test(\\.cc|(_c)?\\.c)$")  # *_test.cc
+  list(FILTER sources EXCLUDE REGEX "^test(\\.cc|(_c)?\\.c)$")  # test.cc
   list(FILTER sources EXCLUDE REGEX "_fuzzer\\.cc$")
 
   file(GLOB_RECURSE headers *.h)