[feat] Improve error message when parameters are undefined

reframe/core/decorators.py

@@ -85,8 +85,8 @@ def _validate_test(cls):
                                  'subclass of RegressionTest')
 
     if (cls.is_abstract()):
-        raise ValueError(f'decorated test ({cls.__qualname__!r}) is an'
-                         f' abstract test')
+        raise ValueError(f'decorated test ({cls.__qualname__!r}) has one or '
+                         f'more undefined parameters')
 
 
 def simple_test(cls):

reframe/core/meta.py

@@ -233,13 +233,12 @@ def param_space(cls):
         return cls._rfm_param_space
 
     def is_abstract(cls):
-        '''Check if the test is an abstract test.
+        '''Check if the class is an abstract test.
 
-        If the parameter space has undefined parameters, the test is considered
-        an abstract test. If that is the case, the length of the parameter
-        space is just 0.
+        This is the case when some parameters are undefined, which results in
+        the length of the parameter space being 0.
 
-        :return: bool indicating wheteher the test is abstract or not
+        :return: bool indicating wheteher the test has undefined parameters.
 
         :meta private:
         '''

unittests/test_parameters.py

@@ -21,6 +21,7 @@ class TwoParams(NoParams):
 
 
 class Abstract(TwoParams):
+    '''An abstract test is a test with undefined parameters.'''
     P0 = parameter()