Show debug log messages on the console in the test when enabled

Using LogEnabler in wxFileSystemWatcher test case still didn't show
anything even in case of unexpected failures because debug messages
didn't appear in the test output.

Fix this by using a custom log target which shows the debug (and trace)
messages on stderr, instead of using the debug output for them, even
under MSW.

Also make LogEnabler public, and rename it to a more unique name, as it
could be useful in the other tests too.

tests/test.cpp

@@ -188,6 +188,71 @@ CATCH_TRANSLATE_EXCEPTION(TestAssertFailure& e)
 
 #endif // wxDEBUG_LEVEL
 
+#if wxUSE_LOG
+
+// Custom log target used while running the tests.
+class TestLogger : public wxLog
+{
+public:
+    TestLogger()
+    {
+        // Use standard time-stamp instead of the locale-specific one and show
+        // milliseconds too.
+        wxLog::SetTimestamp("%Y-%m-%d %H:%M:%S.%l");
+    }
+
+    // This is used by TestLogEnabler to enable logging all messages.
+    static int ms_enableCount;
+
+protected:
+    virtual void DoLogRecord(wxLogLevel level,
+                             const wxString& msg,
+                             const wxLogRecordInfo& info) wxOVERRIDE
+    {
+        // If logging was explicitly enabled, show everything on the console.
+        //
+        // Otherwise we only show trace messages as they are not given by
+        // default and can be only activated by setting WXTRACE.
+        if ( ms_enableCount || level == wxLOG_Trace )
+        {
+            wxString ts;
+            TimeStampMS(&ts, info.timestampMS);
+
+            const wxString levels[] =
+            {
+                "Fatal", "Error", "Warning",
+                "Message", "Status", "Info",
+                "Debug", "Trace", "Progress"
+            };
+            wxString prefix;
+            if ( level < WXSIZEOF(levels) )
+                prefix = levels[level];
+            else
+                prefix.Printf("Level %d", level);
+
+            m_out.Output(wxString::Format("[%s] %s: %s", ts, prefix, msg));
+        }
+    }
+
+    wxMessageOutputStderr m_out;
+};
+
+// By default, normal logging is disabled as it would interfere with the normal
+// test output.
+int TestLogger::ms_enableCount = 0;
+
+TestLogEnabler::TestLogEnabler()
+{
+    TestLogger::ms_enableCount++;
+}
+
+TestLogEnabler::~TestLogEnabler()
+{
+    TestLogger::ms_enableCount--;
+}
+
+#endif // wxUSE_LOG
+
 #if wxUSE_GUI
     typedef wxApp TestAppBase;
     typedef wxGUIAppTraits TestAppTraitsBase;
@@ -602,13 +667,7 @@ bool TestApp::ProcessEvent(wxEvent& event)
 int TestApp::RunTests()
 {
 #if wxUSE_LOG
-    // Switch off logging to avoid interfering with the tests output unless
-    // WXTRACE is set, as otherwise setting it would have no effect while
-    // running the tests.
-    if ( !wxGetEnv(wxASCII_STR("WXTRACE"), NULL) )
-        wxLog::EnableLogging(false);
-    else
-        wxLog::SetTimestamp("%Y-%m-%d %H:%M:%S.%l");
+    delete wxLog::SetActiveTarget(new TestLogger);
 #endif
 
     // Cast is needed under MSW where Catch also provides an overload taking