Example of how to write tests if you vendor dependencies. (#628)

* Make sh tests portable

Author: aiuto

developers.md

@@ -96,3 +96,11 @@ organization will commit to maintaining that feature and responding to issues.
     distribution.
 -   Other new dependencies are strongly discouraged. The exception is that we
     may take dependencies on other modules maintained by the Bazel team.
+
+### Write for vendoring the source tree.
+
+We presume that some users will vendor this entire rule set into their source
+tree and want to test it from their WORKSPACE. Towards that end we try to
+minimize the places where we assume the path to any package is absolute
+from WORKSPACE. See tests/package_naming_aggregate_test.sh for an example
+of how we can write a sh_test that works after re-rooting the sources.

tests/package_naming_aggregate_test.sh

@@ -16,7 +16,10 @@
 # that we get the expected file names.
 set -e
 
-declare -r DATA_DIR="${TEST_SRCDIR}/rules_pkg/tests"
+# Portably find the absolute path to the test data, even if this code has been
+# vendored in to a source tree and re-rooted.
+TEST_PACKAGE="$(echo ${TEST_TARGET} | sed -e 's/:.*$//' -e 's@//@@')"
+declare -r DATA_DIR="${TEST_SRCDIR}/${TEST_WORKSPACE}/${TEST_PACKAGE}"
 
 for pkg in test_naming_some_value.deb test_naming_some_value.tar test_naming_some_value.zip ; do
   ls -l "${DATA_DIR}/$pkg"