update coil test to use average change

tests/test_optimizer.py

@@ -1356,7 +1356,6 @@ def test_quad_flux_with_surface_current_field():
     )
 
 
-@pytest.mark.skip
 @pytest.mark.unit
 def test_optimize_coil_currents(DummyCoilSet):
     """Tests optimization takes step sizes proportional to variable scales."""
@@ -1377,8 +1376,9 @@ def test_optimize_coil_currents(DummyCoilSet):
         verbose=2,
         copy=True,
     )
-    # check that optimized coil currents changed by more than 15% from initial values
+    # check that on average optimized coil currents changed by more than
+    # 15% from initial values
     np.testing.assert_array_less(
-        np.asarray(coils.current) * 0.15,
-        np.abs(np.asarray(coils_opt.current) - np.asarray(coils.current)),
+        np.mean(np.asarray(coils.current) * 0.15),
+        np.mean(np.abs(np.asarray(coils_opt.current) - np.asarray(coils.current))),
     )