gtest.cc: run tests within a test suite in a deterministic order.

Ensure that tests are run in the order specified in the source code, even if
they are registered manually using RegisterTest. There should be no behavior
change for the common case.

PiperOrigin-RevId: 522136303
Change-Id: If155e2666780af0e514fbbf5ff2b157d5fe2fef1

googletest/src/gtest.cc

@@ -44,6 +44,7 @@
 #include <chrono>  // NOLINT
 #include <cmath>
 #include <cstdint>
+#include <cstring>
 #include <initializer_list>
 #include <iomanip>
 #include <ios>
@@ -2981,6 +2982,25 @@ void TestSuite::Run() {
 
   TestEventListener* repeater = UnitTest::GetInstance()->listeners().repeater();
 
+  // Ensure our tests are in a deterministic order.
+  //
+  // We do this by sorting lexicographically on (file, line number), providing
+  // an order matching what the user can see in the source code.
+  //
+  // In the common case the line number comparison shouldn't be necessary,
+  // because the registrations made by the TEST macro are executed in order
+  // within a translation unit. But this is not true of the manual registration
+  // API, and in more exotic scenarios a single file may be part of multiple
+  // translation units.
+  std::stable_sort(test_info_list_.begin(), test_info_list_.end(),
+                   [](const TestInfo* const a, const TestInfo* const b) {
+                     if (const int result = std::strcmp(a->file(), b->file())) {
+                       return result < 0;
+                     }
+
+                     return a->line() < b->line();
+                   });
+
   // Call both legacy and the new API
   repeater->OnTestSuiteStart(*this);
 //  Legacy API is deprecated but still available