diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 347275b6a..be9e175e6 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -100,11 +100,11 @@ git checkout -b my_feature_branch
 After you have made changes on this branch, add and commit them when you are ready:
 
 ```bash
-# lint your code
-black . 
+# black format only the source code
+black fastplotlib/
 
 # run tests from the repo root dir
-WGPU_FORCE_OFFSCREEN=1 pytest tests/
+RENDERCANVAS_FORCE_OFFSCREEN=1 pytest tests/
 
 # desktop examples
 pytest -v examples
@@ -195,6 +195,13 @@ The tests will produce slightly different imperceptible (to a human) results on
 ground-truth. A small RMSE tolerance has been chosen, `0.025` for most examples. If the output image and 
 ground-truth image are within that tolerance the test will pass. 
 
+If the test image and ground-truth image are above the threshold, the test will fail and a difference image will be located in the follow directory:
+
+```
+examples/desktop/diffs
+examples/notebooks/diffs
+```
+
 Some feature development may require the ground-truth screenshots to be updated. In the event that your changes require
 this, please do the following: 
 
@@ -288,12 +295,12 @@ pip install -e ".[imgui, tests, docs, notebook]"
 4) Lint codebase and make sure tests pass 
 
 ```bash
-# lint codebase 
-black .
+# black format only the source code
+black fastplotlib/
 
 # run tests 
 # backend tests 
-WGPU_FORCE_OFFSCREEN=1 pytest tests/
+RENDERCANVAS_FORCE_OFFSCREEN=1 pytest tests/
 
 # desktop examples
 pytest -v examples