t3701: avoid depending on the TTY prerequisite

The TTY prerequisite is a rather heavy one: it not only requires Perl to
work, but also the IO/Pty.pm module (with native support, and it
requires pseudo terminals, too).

In particular, test cases marked with the TTY prerequisite would be
skipped in Git for Windows' SDK.

In the case of `git add -p`, we do not actually need that big a hammer,
as we do not want to test any functionality that requires a pseudo
terminal; all we want is for the interactive add command to use color,
even when being called from within the test suite.

And we found exactly such a trick earlier already: when we added a test
case to verify that the main loop of `git add -i` is colored
appropriately. Let's use that trick instead of the TTY prerequisite.

While at it, we avoid the pipes, as we do not want a SIGPIPE to break
the regression test cases (which will be much more likely when we do not
run everything through Perl because that is inherently slower).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3701-add-interactive.sh

@@ -23,6 +23,17 @@ diff_cmp () {
 	test_cmp "$1.filtered" "$2.filtered"
 }
 
+# This function uses a trick to manipulate the interactive add to use color:
+# the `want_color()` function special-cases the situation where a pager was
+# spawned and Git now wants to output colored text: to detect that situation,
+# the environment variable `GIT_PAGER_IN_USE` is set. However, color is
+# suppressed despite that environment variable if the `TERM` variable
+# indicates a dumb terminal, so we set that variable, too.
+
+force_color () {
+	env GIT_PAGER_IN_USE=true TERM=vt100 "$@"
+}
+
 test_expect_success 'setup (initial)' '
 	echo content >file &&
 	git add file &&
@@ -451,35 +462,38 @@ test_expect_success 'patch mode ignores unmerged entries' '
 	diff_cmp expected diff
 '
 
-test_expect_success TTY 'diffs can be colorized' '
+test_expect_success 'diffs can be colorized' '
 	git reset --hard &&
 
 	echo content >test &&
-	printf y | test_terminal git add -p >output 2>&1 &&
+	printf y >y &&
+	force_color git add -p >output 2>&1 <y &&
 
 	# We do not want to depend on the exact coloring scheme
 	# git uses for diffs, so just check that we saw some kind of color.
 	grep "$(printf "\\033")" output
 '
 
-test_expect_success TTY 'diffFilter filters diff' '
+test_expect_success 'diffFilter filters diff' '
 	git reset --hard &&
 
 	echo content >test &&
 	test_config interactive.diffFilter "sed s/^/foo:/" &&
-	printf y | test_terminal git add -p >output 2>&1 &&
+	printf y >y &&
+	force_color git add -p >output 2>&1 <y &&
 
 	# avoid depending on the exact coloring or content of the prompts,
 	# and just make sure we saw our diff prefixed
 	grep foo:.*content output
 '
 
-test_expect_success TTY 'detect bogus diffFilter output' '
+test_expect_success 'detect bogus diffFilter output' '
 	git reset --hard &&
 
 	echo content >test &&
 	test_config interactive.diffFilter "echo too-short" &&
-	printf y | test_must_fail test_terminal git add -p
+	printf y >y &&
+	test_must_fail force_color git add -p <y
 '
 
 test_expect_success 'patch-mode via -i prompts for files' '
@@ -689,7 +703,7 @@ test_expect_success 'show help from add--helper' '
 	<BOLD;BLUE>What now<RESET>>$SP
 	Bye.
 	EOF
-	test_write_lines h | GIT_PAGER_IN_USE=true TERM=vt100 git add -i >actual.colored &&
+	test_write_lines h | force_color git add -i >actual.colored &&
 	test_decode_color <actual.colored >actual &&
 	test_i18ncmp expect actual
 '