[PATCH v2 2/2] test-lib: introduce required prereq for test runs

[Fabian Stelzer <fs@gigacodes.de>]

In certain environments or for specific test scenarios we might expect a
specific prerequisite check to succeed. Therefore we would like to
trigger an error when running our tests if this is not the case.

To remedy this we add the environment variable GIT_TEST_REQUIRE_PREREQ
which can be set to a comma separated list of prereqs. If one of these
prereq tests fail then the whole test run will abort.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
---
 t/README                |  6 ++++++
 t/test-lib-functions.sh | 11 +++++++++++
 2 files changed, 17 insertions(+)

diff --git a/t/README b/t/README
index 29f72354bf..18ce75976e 100644
--- a/t/README
+++ b/t/README
@@ -466,6 +466,12 @@ explicitly providing repositories when accessing submodule objects is
 complete or needs to be abandoned for whatever reason (in which case the
 migrated codepaths still retain their performance benefits).
 
+GIT_TEST_REQUIRE_PREREQ=<list> allows specifying a comma speparated list of
+prereqs that are required to succeed. If a prereq in this list is triggered by
+a test and then fails then the whole test run will abort. This can help to make
+sure the expected tests are executed and not silently skipped when their
+dependency breaks or is simply not present in a new environment.
+
 Naming Tests
 ------------
 
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index eef2262a36..2c8abf3420 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -680,6 +680,17 @@ test_have_prereq () {
 			# Keep a list of missing prerequisites; restore
 			# the negative marker if necessary.
 			prerequisite=${negative_prereq:+!}$prerequisite
+
+			# Abort if this prereq was marked as required
+			if test -n $GIT_TEST_REQUIRE_PREREQ
+			then
+				case ",$GIT_TEST_REQUIRE_PREREQ," in
+				*,$prerequisite,*)
+					error "required prereq $prerequisite failed"
+					;;
+				esac
+			fi
+
 			if test -z "$missing_prereq"
 			then
 				missing_prereq=$prerequisite
-- 
2.31.1