Fix test assertion message

Change-Id: Ifd9f50a68e5dd40003cd1bd32a5b806b0282ce44

test/source/screenshot_test.cxx

@@ -74,7 +74,7 @@ void ScreenshotTest::implSaveScreenshot(const Bitmap& rScreenshot, const OString
 
     OUString aFullPath = m_directories.getPathFromWorkdir(OUStringToOString(aDirname + "/" + aBasename + ".png",RTL_TEXTENCODING_UTF8).getStr());
     SvFileStream aNew(aFullPath, StreamMode::WRITE | StreamMode::TRUNC);
-    CPPUNIT_ASSERT_MESSAGE(OUStringToOString("Failed to open " + OUString::number(sal_uInt32(aNew.GetErrorCode())), RTL_TEXTENCODING_UTF8).getStr(), aNew.IsOpen());
+    CPPUNIT_ASSERT_MESSAGE(OUStringToOString("Failed to open <" + aFullPath + ">: " + OUString::number(sal_uInt32(aNew.GetErrorCode())), RTL_TEXTENCODING_UTF8).getStr(), aNew.IsOpen());
 
     vcl::PNGWriter aPNGWriter(rScreenshot);
     aPNGWriter.Write(aNew);