ITS: improve test_param_exposure_time.py logging & errors

bug: 221245589
Change-Id: Ie96e48fa70fdef37f715961ce2f8b9f816ae798b
diff --git a/apps/CameraITS/tests/scene1_1/test_param_exposure_time.py b/apps/CameraITS/tests/scene1_1/test_param_exposure_time.py
index 446003e..5cfa5a5 100644
--- a/apps/CameraITS/tests/scene1_1/test_param_exposure_time.py
+++ b/apps/CameraITS/tests/scene1_1/test_param_exposure_time.py
@@ -82,6 +82,7 @@
         patch = image_processing_utils.get_image_patch(
             img, PATCH_X, PATCH_Y, PATCH_W, PATCH_H)
         rgb_means = image_processing_utils.compute_image_means(patch)
+        logging.debug('RGB means: %s', str(rgb_means))
         exp_times.append(e * e_mult)
         r_means.append(rgb_means[0])
         g_means.append(rgb_means[1])
@@ -102,8 +103,9 @@
     for ch, means in enumerate([r_means, g_means, b_means]):
       for i in range(len(EXP_MULT_FACTORS)-1):
         if means[i+1] <= means[i]:
-          raise AssertionError(
-              f'{COLORS[ch]} [i+1]: {means[i+1]:.4f}, [i]: {means[i]:.4f}')
+          raise AssertionError(f'{COLORS[ch]} not increasing in brightness! '
+                               f'{COLORS[ch]}[i+1]: {means[i+1]:.4f}, '
+                               f'{COLORS[ch]}[i]: {means[i]:.4f}')
 
 if __name__ == '__main__':
   test_runner.main()