t4030: demonstrate behavior of show with textconv

"git show <commit>" honors the --textconv option while "git show <blob>"
does not. Demonstrate this in the test.

Since the current behavior is supposed to stay as is, we expect the
default for "git show <blob>" to remain --no-textconv.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4030-diff-textconv.sh

@@ -58,6 +58,12 @@ test_expect_success 'diff produces text' '
 	test_cmp expect.text actual
 '
 
+test_expect_success 'show commit produces text' '
+	git show HEAD >diff &&
+	find_diff <diff >actual &&
+	test_cmp expect.text actual
+'
+
 test_expect_success 'diff-tree produces binary' '
 	git diff-tree -p HEAD^ HEAD >diff &&
 	find_diff <diff >actual &&
@@ -84,6 +90,24 @@ test_expect_success 'status -v produces text' '
 	git reset --soft HEAD@{1}
 '
 
+test_expect_success 'show blob produces binary' '
+	git show HEAD:file >actual &&
+	printf "\\0\\n\\01\\n" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_failure 'show --textconv blob produces text' '
+	git show --textconv HEAD:file >actual &&
+	printf "0\\n1\\n" >expect &&
+	test_cmp expect actual
+'
+
+test_success 'show --no-textconv blob produces binary' '
+	git show --textconv HEAD:file >actual &&
+	printf "\\0\\n\\01\\n" >expect &&
+	test_cmp expect actual
+'
+
 test_expect_success 'grep-diff (-G) operates on textconv data (add)' '
 	echo one >expect &&
 	git log --root --format=%s -G0 >actual &&