stash: add tests for git stash show config

This commit introduces tests for `git stash show`
config. It tests all the cases where `stash.showStat`
and `stash.showPatch` are unset or set to true / false.

Signed-off-by: Paul-Sebastian Ungureanu <ungureanupaulsebastian@gmail.com>

t/t3907-stash-show-config.sh

@@ -0,0 +1,81 @@
+#!/bin/sh
+
+test_description='Test git stash show configuration.'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit file
+'
+
+# takes three parameters:
+# 1. the stash.showStat value (or "<unset>")
+# 2. the stash.showPatch value (or "<unset>")
+# 3. the diff options of the expected output (or nothing for no output)
+test_stat_and_patch () {
+	if test "<unset>" = "$1"
+	then
+		test_might_fail git config --unset stash.showStat
+	else
+		test_config stash.showStat "$1"
+	fi &&
+
+	if test "<unset>" = "$2"
+	then
+		test_might_fail git config --unset stash.showPatch
+	else
+		test_config stash.showPatch "$2"
+	fi &&
+
+	shift &&
+	shift &&
+	echo 2 >file.t &&
+	git diff "$@" >expect &&
+	git stash &&
+	git stash show >actual &&
+
+	if test -z "$1"
+	then
+		test_must_be_empty actual
+	else
+		test_cmp expect actual
+	fi
+}
+
+test_expect_success 'showStat unset showPatch unset' '
+	test_stat_and_patch "<unset>" "<unset>" --stat
+'
+
+test_expect_success 'showStat unset showPatch false' '
+	test_stat_and_patch "<unset>" false --stat
+'
+
+test_expect_success 'showStat unset showPatch true' '
+	test_stat_and_patch "<unset>" true --stat -p
+'
+
+test_expect_success 'showStat false showPatch unset' '
+	test_stat_and_patch false "<unset>"
+'
+
+test_expect_success 'showStat false showPatch false' '
+	test_stat_and_patch false false
+'
+
+test_expect_success 'showStat false showPatch true' '
+	test_stat_and_patch false true -p
+'
+
+test_expect_success 'showStat true showPatch unset' '
+	test_stat_and_patch true "<unset>" --stat
+'
+
+test_expect_success 'showStat true showPatch false' '
+	test_stat_and_patch true false --stat
+'
+
+test_expect_success 'showStat true showPatch true' '
+	test_stat_and_patch true true --stat -p
+'
+
+test_done