Add option to warn when no tests ran

Closes #1158

include/internal/catch_session.cpp

@@ -18,6 +18,7 @@
 #include "catch_random_number_generator.h"
 #include "catch_startup_exception_registry.h"
 #include "catch_text.h"
+#include "catch_stream.h"
 
 #include <cstdlib>
 #include <iomanip>
@@ -80,6 +81,20 @@ namespace Catch {
                     context.reporter().skipTest(testCase);
             }
 
+            if (config->warnAboutNoTests() && totals.testCases.total() == 0) {
+                ReusableStringStream testConfig;
+
+                bool first = true;
+                for (const auto& input : config->getTestsOrTags()) {
+                    if (!first) { testConfig << ' '; }
+                    first = false;
+                    testConfig << input;
+                }
+
+                context.reporter().noMatchingTestCases(testConfig.str());
+                totals.error = -1;
+            }
+
             context.testGroupEnded(config->name(), totals, 1, 1);
             return totals;
         }
@@ -259,10 +274,11 @@ namespace Catch {
             if( Option<std::size_t> listed = list( config() ) )
                 return static_cast<int>( *listed );
 
+            auto totals = runTests( m_config );
             // Note that on unices only the lower 8 bits are usually used, clamping
             // the return value to 255 prevents false negative when some multiple
             // of 256 tests has failed
-            return (std::min)( MaxExitCode, static_cast<int>( runTests( m_config ).assertions.failed ) );
+            return (std::min)( { MaxExitCode, totals.error, static_cast<int>( totals.assertions.failed ) } );
         }
         catch( std::exception& ex ) {
             Catch::cerr() << ex.what() << std::endl;