[test] fix empty CIRCLE_COMPARE_URL

.circleci/config.yml

@@ -48,12 +48,18 @@ jobs:
     steps:
       - checkout
       - *restore_repo
+      - run:
+          name: Setup Environment Variables
+          command: |
+            # https://circleci.com/docs/2.0/env-vars/#setting-an-environment-variable-in-a-shell-command
+            echo 'export COMPARE_URL="$CIRCLE_COMPARE_URL"' >> $BASH_ENV
       - run:
           name: Check if yarn prettier was run
           command: |
+
             # commit range between master and branch
             # CIRCLE_COMPARE_URL=https://github.com/org/repo/compare/sha1...sha1
-            COMMIT_RANGE=$(grep -oP "\w+\.\.\.\w+" <<< "$CIRCLE_COMPARE_URL")
+            COMMIT_RANGE=$(grep -oP "\w+\.\.\.\w+" <<< "$COMPARE_URL")
             # Files changed on this branch
             CHANGED_FILES=$(git diff --name-only "$COMMIT_RANGE")
             # if we use an empty string as a pattern grep will match everything