[PATCH 2/2] t0303: resurrect commit message as test documentation

["Zbigniew Jędrzejewski-Szmek" <zbyszek@in.waw.pl>]

The commit message which added those tests (861444f 't: add test
harness for external credential helpers' 2011-12-10) provided nice
documentation in the commit message. Let's make it more visible.

Signed-off-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
---
 t/t0303-credential-external.sh |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/t/t0303-credential-external.sh b/t/t0303-credential-external.sh
index f1e0e75..4ab9a54 100755
--- a/t/t0303-credential-external.sh
+++ b/t/t0303-credential-external.sh
@@ -1,5 +1,23 @@
 #!/bin/sh
 
+# Test harness for external credential helpers
+#
+# This is a tool for authors of external helper tools to sanity-check
+# their helpers. If you have written the "git-credential-foo" helper,
+# you check it with:
+#
+# GIT_TEST_CREDENTIAL_HELPER=foo make t0303-credential-external.sh
+#
+# This assumes that your helper is capable of both storing and
+# retrieving credentials (some helpers may be read-only, and
+# they will fail these tests).
+#
+# If your helper supports time-based expiration with a
+# configurable timeout, you can test that feature with:
+#
+#  GIT_TEST_CREDENTIAL_HELPER_TIMEOUT="foo --timeout=1" \
+#      make t0303-credential-external.sh
+
 test_description='external credential helper tests'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-credential.sh
-- 
1.7.9.3.467.g8f1c7