Check all workspaces in workspace group

Refs #21214

Testing/SystemTests/tests/analysis/ISIS_PowderPolarisTest.py

@@ -54,8 +54,8 @@ class CreateVanadiumTest(stresstesting.MantidStressTest):
 
     def validate(self):
         splined_ws, unsplined_ws = self.calibration_results
-        self.assertEqual(unsplined_ws[0].sample().getMaterial().name(), 'V')
-        self.assertEqual(splined_ws[0].sample().getMaterial().name(), 'V')
+        for ws in splined_ws+unsplined_ws:
+            self.assertEqual(ws.sample().getMaterial().name(), 'V')
         return (unsplined_ws.getName(), "ISIS_Powder-POLARIS00098533_unsplined.nxs",
                 splined_ws.getName(), "ISIS_Powder-POLARIS00098533_splined.nxs")
 
@@ -82,7 +82,8 @@ class FocusTest(stresstesting.MantidStressTest):
         self.focus_results = run_focus()
 
     def validate(self):
-        self.assertEqual(self.focus_results[0].sample().getMaterial().name(), 'Si')
+        for ws in self.focus_results:
+            self.assertEqual(ws.sample().getMaterial().name(), 'Si')
         return self.focus_results.getName(), "ISIS_Powder-POLARIS98533_FocusSempty.nxs"
 
     def cleanup(self):