test-suite: add image_diff_is_failure() function

This cleans the code and fixes a boolean logic error where this check
was done manually.

1 files changed, 8 insertions, 0 deletions

diff --git a/test/buffer-diff.c b/test/buffer-diff.c
index 8fc3f891e..087ac459b 100644
--- a/test/buffer-diff.c
+++ b/test/buffer-diff.c
@@ -252,3 +252,11 @@ image_diff (const cairo_test_context_t *ctx,
 
     return CAIRO_STATUS_SUCCESS;
 }
+
+cairo_bool_t
+image_diff_is_failure (const buffer_diff_result_t *result,
+                       unsigned int                tolerance)
+{
+  return result->pixels_changed &&
+         result->max_diff > tolerance;
+}