Fix tests on metrics

Author: oscgonfer

scdata/device/device.py

@@ -557,7 +557,9 @@ def process(self, only_new=False, metrics_list=None):
                         process_ok &= True
                     elif 'SUCCESS' in process_result.status_code.name:
                         if isinstance(process_result.data, DataFrame):
-                           for col in process_result.data.columns:
+                            if len(process_result.data.columns) == 1:
+                                self.data[f'{metric.name}'] = process_result.data
+                            for col in process_result.data.columns:
                                 if 'conc' in col:
                                     self.data[f'{metric.name}'] = process_result.data[col]
                                 else: