diff --git a/eessi/testsuite/eessi_mixin.py b/eessi/testsuite/eessi_mixin.py
index deffcd0d..961312e6 100644
--- a/eessi/testsuite/eessi_mixin.py
+++ b/eessi/testsuite/eessi_mixin.py
@@ -1,13 +1,11 @@
-from reframe.core.builtins import variable, parameter, run_after
-from reframe.core.exceptions import ReframeSyntaxError
+from reframe.core.builtins import parameter, run_after
+from reframe.core.exceptions import ReframeFatalError
 from reframe.core.pipeline import RegressionMixin
 from reframe.utility.sanity import make_performance_function
 
 from eessi.testsuite import hooks
 from eessi.testsuite.constants import DEVICE_TYPES, SCALES, COMPUTE_UNIT
 
-from eessi.testsuite import __version__ as EESSI_TESTSUITE_VERSION
-
 
 # Hooks from the Mixin class seem to be executed _before_ those of the child class
 # Thus, if the Mixin class needs self.X to be defined in after setup, the child class would have to define it before
@@ -34,12 +32,8 @@ class EESSI_Mixin(RegressionMixin):
     """
 
     # Current version of the EESSI test suite
-    eessi_testsuite_version = variable(str, value=EESSI_TESTSUITE_VERSION)
 
     measure_memory_usage = False
-#    valid_prog_environs = ['default']
-#    valid_systems = ['*']
-#    time_limit = '30m'
     scale = parameter(SCALES.keys())
 
     # Note that the error for an empty parameter is a bit unclear for ReFrame 4.6.2, but that will hopefully improve
@@ -47,6 +41,14 @@ class EESSI_Mixin(RegressionMixin):
     # If that improves: uncomment the following to force the user to set module_name
     # module_name = parameter()
 
+    def __init_subclass__(cls, **kwargs):
+        " set default values for built-in ReFrame attributes "
+        super().__init_subclass__(**kwargs)
+        cls.valid_prog_environs = ['default']
+        cls.valid_systems = ['*']
+        if not cls.time_limit:
+            cls.time_limit = '1h'
+
     # Helper function to validate if an attribute is present it item_dict.
     # If not, print it's current name, value, and the valid_values
     def validate_item_in_dict(self, item, item_dict, check_keys=False):
@@ -62,9 +64,11 @@ def validate_item_in_dict(self, item, item_dict, check_keys=False):
 
         value = getattr(self, item)
         if value not in valid_items:
-            valid_items_str = (', '.join("'" + item + "'" for item in valid_items))
-            msg = "The variable '%s' had value '%s', but the only valid values are %s" % (item, value, valid_items_str)
-            raise ReframeSyntaxError(msg)
+            if len(valid_items) == 1:
+                msg = f"The variable '{item}' has value {value}, but the only valid value is {valid_items[0]}"
+            else:
+                msg = f"The variable '{item}' has value {value}, but the only valid values are {valid_items}"
+            raise ReframeFatalError(msg)
 
     # We have to make sure that these gets set in any test that inherits
     # device_type = variable(str)
@@ -80,12 +84,14 @@ def validate_init(self):
             if not hasattr(self, var):
                 msg = "The variable '%s' should be defined in any test class that inherits" % var
                 msg += " from EESSI_Mixin in the init phase (or earlier), but it wasn't"
-                raise ReframeSyntaxError(msg)
+                raise ReframeFatalError(msg)
 
         # Check that the value for these variables is valid,
         # i.e. exists in their respective dict from eessi.testsuite.constants
         self.validate_item_in_dict('device_type', DEVICE_TYPES)
         self.validate_item_in_dict('scale', SCALES, check_keys=True)
+        self.validate_item_in_dict('valid_systems', {'valid_systems': ['*']})
+        self.validate_item_in_dict('valid_prog_environs', {'valid_prog_environs': ['default']})
 
     @run_after('init')
     def run_after_init(self):
@@ -117,7 +123,7 @@ def validate_setup(self):
             if not hasattr(self, var):
                 msg = "The variable '%s' should be defined in any test class that inherits" % var
                 msg += " from EESSI_Mixin in the setup phase (or earlier), but it wasn't"
-                raise ReframeSyntaxError(msg)
+                raise ReframeFatalError(msg)
 
         # Check if mem_func was defined to compute the required memory per node as function of the number of
         # tasks per node
@@ -126,7 +132,7 @@ def validate_setup(self):
             msg += " from EESSI_Mixin in the setup phase (or earlier), but it wasn't. Note that this function"
             msg += " can use self.num_tasks_per_node, as it will be called after that attribute"
             msg += " has been set."
-            raise ReframeSyntaxError(msg)
+            raise ReframeFatalError(msg)
 
         # Check that the value for these variables is valid
         # i.e. exists in their respective dict from eessi.testsuite.constants
diff --git a/eessi/testsuite/tests/apps/lammps/lammps.py b/eessi/testsuite/tests/apps/lammps/lammps.py
index 607ed361..22e70d3e 100644
--- a/eessi/testsuite/tests/apps/lammps/lammps.py
+++ b/eessi/testsuite/tests/apps/lammps/lammps.py
@@ -12,10 +12,7 @@
 
 
 class EESSI_LAMMPS_base(rfm.RunOnlyRegressionTest, EESSI_Mixin):
-    valid_prog_environs = ['default']
-    valid_systems = ['*']
     time_limit = '30m'
-
     device_type = parameter([DEVICE_TYPES[CPU], DEVICE_TYPES[GPU]])
 
     # Parameterize over all modules that start with LAMMPS