Re: [PATCH v2 3/4] t7800: modernize tests

Eliminate a lot of redundant work by using test_config().
Catch more return codes by more use of temporary files
and test_cmp.

The original tests relied upon restore_test_defaults()
from the previous test to provide the next test with a sane
environment.  Make the tests do their own setup so that they
are not dependent on the success of the previous test.
The end result is shorter tests and better test isolation.

Signed-off-by: David Aguilar <redacted>
---
We no longer export variables into the environment per Jonathan's
suggestion.  This covers all of the review notes.

 t/t7800-difftool.sh | 360 ++++++++++++++++++++++++----------------------------
 1 file changed, 165 insertions(+), 195 deletions(-)

diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
index 5b5939b..b577c01 100755
--- a/t/t7800-difftool.sh
+++ b/t/t7800-difftool.sh

@@ -10,29 +10,11 @@ Testing basic diff tool invocation
 
 . ./test-lib.sh
 
+difftool_test_setup()
 {
+	test_config diff.tool test-tool &&
+	test_config difftool.test-tool.cmd 'cat $LOCAL' &&
+	test_config difftool.bogus-tool.cmd false
 }

@@ -324,26 +294,26 @@ test_expect_success PERL 'setup with 2 files different' '
 '
 
 test_expect_success PERL 'say no to the first file' '
-	diff=$( (echo n; echo) | git difftool -x cat branch ) &&
-
-	echo "$diff" | stdin_contains m2 &&
-	echo "$diff" | stdin_contains br2 &&
-	echo "$diff" | stdin_doesnot_contain master &&
-	echo "$diff" | stdin_doesnot_contain branch
+	(echo n && echo) >input &&
+	git difftool -x cat branch <input >output &&
+	cat output | stdin_contains m2 &&
+	cat output | stdin_contains br2 &&
+	cat output | stdin_doesnot_contain master &&
+	cat output | stdin_doesnot_contain branch