Eco account unit tests

* adds eco account unit tests
* adds validity check to eco account form to check on existing deductions and potential conflict with reduced deductable surface
* improves geojson handling on SimpleGeomForm
* adds/updates translation

compensation/forms/eco_account.py

@@ -172,6 +172,23 @@ class EditEcoAccountForm(NewEcoAccountForm):
             disabled_fields
         )
 
+    def is_valid(self):
+        valid = super().is_valid()
+
+        deductable_surface = self.cleaned_data.get("surface")
+        deduction_surface_sum = self.instance.get_deductions_surface()
+        if deductable_surface < deduction_surface_sum:
+            self.add_error(
+                "surface",
+                _("{}m² have been deducted from this eco account so far. The given value of {} would be too low.").format(
+                    deduction_surface_sum,
+                    deductable_surface
+                )
+            )
+            valid &= False
+
+        return valid
+
     def save(self, user: User, geom_form: SimpleGeomForm):
         with transaction.atomic():
             # Fetch data from cleaned POST values