Add return code constants to API

docs/own-main.md

@@ -63,11 +63,12 @@ int main( int argc, char* argv[] ) {
   // overrides command line args
   // only do this if you know you need to
 
-  int numFailed = session.run();
+  returnCode = session.run();
+
+  // returnCode encodes the type of error that occured. See the
+  // integer constants in catch_session.hpp for more information
+  // on what each return code means.
 
-  // numFailed is clamped to 255 as some unices only use the lower 8 bits.
-  // This clamping has already been applied, so just return it here
-  // You can also do any post run clean-up here
   return numFailed;
 }
 ```

src/catch2/catch_session.cpp

@@ -33,14 +33,6 @@
 namespace Catch {
 
     namespace {
-        static constexpr int TestFailureExitCode = 42;
-        static constexpr int UnspecifiedErrorExitCode = 1;
-        static constexpr int AllTestsSkippedExitCode = 4;
-        static constexpr int NoTestsRunExitCode = 2;
-        static constexpr int UnmatchedTestSpecExitCode = 3;
-        static constexpr int InvalidTestSpecExitCode = 5;
-
-
         IEventListenerPtr createReporter(std::string const& reporterName, ReporterConfig&& config) {
             auto reporter = Catch::getRegistryHub().getReporterRegistry().create(reporterName, CATCH_MOVE(config));
             CATCH_ENFORCE(reporter, "No reporter registered with name: '" << reporterName << '\'');

src/catch2/catch_session.hpp

@@ -16,6 +16,14 @@
 
 namespace Catch {
 
+    // TODO: Use C++17 `inline` variables
+    constexpr int UnspecifiedErrorExitCode = 1;
+    constexpr int NoTestsRunExitCode = 2;
+    constexpr int UnmatchedTestSpecExitCode = 3;
+    constexpr int AllTestsSkippedExitCode = 4;
+    constexpr int InvalidTestSpecExitCode = 5;
+    constexpr int TestFailureExitCode = 42;
+
     class Session : Detail::NonCopyable {
     public: