set PUDB_TTY during test, to aid debugging

maybe you don't want this, but it's nice for me and won't harm anything

test.sh

@@ -13,6 +13,12 @@ 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]
@@ -27,7 +33,7 @@ fi
 
 cat "test/${PYTHON_VERSION}_unformatted.py" | python3 cblack.py -q - > test/${PYTHON_VERSION}_reformatted.py
 
-diff -u --color=auto 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