Merging pull request 2211

Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

* https://github.com/avocado-framework/avocado:
  Loader: be clear about the meaning of NOT_A_TEST

avocado/core/loader.py

@@ -499,8 +499,8 @@ class FileLoader(TestLoader):
     """
 
     name = 'file'
-    __not_test_str = ("Does not look like an INSTRUMENTED test, nor is it "
-                      "executable")
+    __not_test_str = ("Not an INSTRUMENTED (avocado.Test based), PyUNITTEST ("
+                      "unittest.TestCase based) or SIMPLE (executable) test")
 
     def __init__(self, args, extra_params):
         test_type = extra_params.pop('allowed_test_types', None)