ci: run test round with parallel-checkout enabled

We already have tests for the basic parallel-checkout operations. But
this code can also run be executed by other commands, such as
git-read-tree and git-sparse-checkout, which are currently not tested
with multiple workers. To promote a wider test coverage without
duplicating tests:

1. Add the GIT_TEST_CHECKOUT_WORKERS environment variable, to optionally
   force parallel-checkout execution during the whole test suite.

2. Set this variable (with a value of 2) in the second test round of our
   linux-gcc CI job. This round runs `make test` again with some
   optional GIT_TEST_* variables enabled, so there is no additional
   overhead in exercising the parallel-checkout code here.

Note that tests checking out less than two parallel-eligible entries
will fall back to the sequential mode. Nevertheless, it's still a good
exercise for the parallel-checkout framework as the fallback codepath
also writes the queued entries using the parallel-checkout functions
(only without spawning any worker).

Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/ci/run-build-and-tests.sh b/ci/run-build-and-tests.sh
index a66b5e8c75..23b28e7391 100755
--- a/ci/run-build-and-tests.sh
+++ b/ci/run-build-and-tests.sh
@@ -25,6 +25,7 @@ linux-gcc)
 	export GIT_TEST_ADD_I_USE_BUILTIN=1
 	export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=master
 	export GIT_TEST_WRITE_REV_INDEX=1
+	export GIT_TEST_CHECKOUT_WORKERS=2
 	make test
 	;;
 linux-clang)