[PATCH v2 4/5] tests: do not require Git to be built when testing an installed Git

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

We really only need the test helpers to be built in the worktree in that
case, but that is not what we test for.

On the other hand it is a perfect opportunity to verify that
`GIT_TEST_INSTALLED` points to a working Git.

So let's test the appropriate Git executable. While at it, also adjust
the error message in the `GIT_TEST_INSTALLED` case.

This patch is best viewed with `-w --patience`.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 t/test-lib.sh | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/t/test-lib.sh b/t/test-lib.sh
index 93883580a8..3d3a65ed0e 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -51,10 +51,15 @@ export LSAN_OPTIONS
 
 ################################################################
 # It appears that people try to run tests without building...
-"$GIT_BUILD_DIR/git" >/dev/null
+"${GIT_TEST_INSTALLED:-$GIT_BUILD_DIR}/git" >/dev/null
 if test $? != 1
 then
-	echo >&2 'error: you do not seem to have built git yet.'
+	if test -n "$GIT_TEST_INSTALLED"
+	then
+		echo >&2 "error: there is no working Git at '$GIT_TEST_INSTALLED'"
+	else
+		echo >&2 'error: you do not seem to have built git yet.'
+	fi
 	exit 1
 fi
 
-- 
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