[PATCH 01/15] read-cache.c: make $GIT_TEST_SPLIT_INDEX boolean

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

While at there, document about this special mode when running the test
suite.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 ci/run-build-and-tests.sh |  2 +-
 read-cache.c              |  4 ++--
 t/README                  | 11 +++++++++++
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/ci/run-build-and-tests.sh b/ci/run-build-and-tests.sh
index 3735ce413f..8190a753de 100755
--- a/ci/run-build-and-tests.sh
+++ b/ci/run-build-and-tests.sh
@@ -11,7 +11,7 @@ make --jobs=2
 make --quiet test
 if test "$jobname" = "linux-gcc"
 then
-	GIT_TEST_SPLIT_INDEX=YesPlease make --quiet test
+	GIT_TEST_SPLIT_INDEX=yes make --quiet test
 fi
 
 check_unignored_build_artifacts
diff --git a/read-cache.c b/read-cache.c
index 10f1c6bb8a..fa3df2e72e 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2268,7 +2268,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 
 	if (!istate->version) {
 		istate->version = get_index_format_default();
-		if (getenv("GIT_TEST_SPLIT_INDEX"))
+		if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0))
 			init_split_index(istate);
 	}
 
@@ -2559,7 +2559,7 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
 		goto out;
 	}
 
-	if (getenv("GIT_TEST_SPLIT_INDEX")) {
+	if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0)) {
 		int v = si->base_sha1[0];
 		if ((v & 15) < 6)
 			istate->cache_changed |= SPLIT_INDEX_ORDERED;
diff --git a/t/README b/t/README
index 24ddebfabf..d5e0a3c786 100644
--- a/t/README
+++ b/t/README
@@ -293,6 +293,17 @@ and know what setup is needed for it.  Or when you want to run
 everything up to a certain test.
 
 
+Running tests with special setups
+---------------------------------
+
+The whole test suite could be run to test some special features
+that cannot be easily covered by a few specific test cases. These
+could be enabled by running the test suite with correct GIT_TEST_
+environment set.
+
+GIT_TEST_SPLIT_INDEX=<boolean> forces split-index mode on the whole
+test suite. Accept any boolean values that are accepted by git-config.
+
 Naming Tests
 ------------
 
-- 
2.17.0.367.g5dd2e386c3