[feat] Add convenience function to set a test variable only if it's undefined

docs/regression_test_api.rst

@@ -670,7 +670,6 @@ Therefore, classes that derive from the base :class:`~reframe.core.pipeline.Regr
 .. automethod:: reframe.core.pipeline.RegressionMixin.variant_name
 
 
-
 ------------------------
 Environments and Systems
 ------------------------

reframe/core/meta.py

@@ -832,13 +832,12 @@ def fixture_space(cls):
     def is_abstract(cls):
         '''Check if the class is an abstract test.
 
-        This is the case when some parameters are undefined, which results in
-        the length of the parameter space being 0.
+        A test is considered abstract if any of its direct or indirect
+        parameters (inherited from a base class or from a fixture) is
+        undefined.
 
-        :return: bool indicating whether the test or any of its fixtures has
-          undefined parameters.
+        :returns: :obj:`True` if the test is abstract, :obj:`False` otherwise.
 
-        :meta private:
         '''
         return cls.num_variants == 0
 
@@ -908,6 +907,8 @@ class HelloTest(rfm.RunOnlyRegressionTest):
     :param kwargs: Any keyword arguments to be passed to the
         :class:`RegressionTestMeta` metaclass.
 
+    .. versionadded:: 3.10.0
+
     '''
     namespace = RegressionTestMeta.__prepare__(name, bases, **kwargs)
     namespace.update(body)

reframe/core/pipeline.py

@@ -1166,6 +1166,26 @@ def fixture_variant(self):
         '''
         return getattr(self, '_rfm_fixt_variant', None)
 
+    def set_var_default(self, name, value):
+        '''Set the default value of a variable if variable is undefined.
+
+        A variable is undefined if it is declared and required and no value is
+        yet assigned to it.
+
+        :param name: The name of the variable.
+        :param value: The value to set the variable to.
+        :raises ValueError: If the variable does not exist
+
+        .. versionadded:: 3.10.1
+
+        '''
+        var_space = type(self).var_space
+        if name not in var_space:
+            raise ValueError(f'no such variable: {name!r}')
+
+        if not var_space[name].is_defined():
+            setattr(self, name, value)
+
     @property
     def perfvalues(self):
         return util.MappingView(self._perfvalues)

unittests/test_pipeline.py

@@ -1527,6 +1527,24 @@ def validate(self):
     _run(hello_cls(), *local_exec_ctx)
 
 
+def test_set_var_default():
+    class _X(rfm.RunOnlyRegressionTest):
+        foo = variable(int, value=10)
+        bar = variable(int)
+
+        @run_after('init')
+        def set_defaults(self):
+            self.set_var_default('foo', 100)
+            self.set_var_default('bar', 100)
+
+            with pytest.raises(ValueError):
+                self.set_var_default('foobar', 10)
+
+    x = _X()
+    assert x.foo == 10
+    assert x.bar == 100
+
+
 def test_set_name_deprecation():
     from reframe.core.warnings import ReframeDeprecationWarning