add a note to developer guide about PYTHONPATH

The test suite does not currently rely on the installed Graphviz Python bindings
being findable and usable. However in future test cases may be introduced that
do. This change future proofs the instructions against an update like this.
Related to #1992.

diff --git a/DEVELOPERS.md b/DEVELOPERS.md
index 5404a041fe5cbd06042710548f0a6cada84faab7..960b0cd3e8d437669f975a154b1491c6cbe7a66e 100644 (file)
--- a/DEVELOPERS.md
+++ b/DEVELOPERS.md
@@ -258,6 +258,7 @@ follows:
 # run the Graphviz test suite, making the temporary installation visible to it
 env PATH=${PREFIX}/bin:${PATH} C_INCLUDE_PATH=${PREFIX}/include \
   LD_LIBRARY_PATH=${PREFIX}/lib LIBRARY_PATH=${PREFIX}/lib \
+  PYTHONPATH=${PREFIX}/lib/graphviz/python3 \
   python3 -m pytest tests rtest --verbose
 ```