diff --git a/test.sh b/test.sh
index 83e2e62..982cffe 100755
--- a/test.sh
+++ b/test.sh
@@ -13,9 +13,27 @@ err_report() {
 
 trap 'err_report' ERR
 
+if tty --quiet; then
+  # enable debugging with [PuDB](https://youtu.be/bJYkCWPs_UU)
+  export PUDB_TTY
+  PUDB_TTY="$(tty)"
+fi
+
+PYTHON_VERSION2="$(python3 -c 'if True:
+    import sys
+    major, minor = sys.version_info[:2]
+    print(major, minor, sep=".")
+')"
+
+if [[ $PYTHON_VERSION != $PYTHON_VERSION2 ]]; then
+  echo >&2 \
+    "wrong python version! (found $PYTHON_VERSION2 expected $PYTHON_VERSION)" \
+  exit 1
+fi
+
 cat "test/${PYTHON_VERSION}_unformatted.py" | python3 cblack.py -q - > test/${PYTHON_VERSION}_reformatted.py
 
-diff test/${PYTHON_VERSION}_expected.py test/${PYTHON_VERSION}_reformatted.py
+diff -u --color=always test/${PYTHON_VERSION}_expected.py test/${PYTHON_VERSION}_reformatted.py
 
 echo "Test ${PYTHON_VERSION} Succeeded!"
 exit 0