t1006: modernize test style to use `test_cmp`

The tests for git-cat-file(1) are quite old and haven't ever been
updated since they were introduced. They thus tend to use old idioms
that have since grown outdated. Most importantly, many of the tests use
`test $A = $B` to compare expected and actual output. This has the
downside that it is impossible to tell what exactly is different between
both versions in case the test fails.

Refactor the tests to instead use `test_cmp`. While more verbose, it
both tends to be more readable and will result in a nice diff in case
states don't match.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t1006-cat-file.sh

@@ -296,9 +296,11 @@ tag_size=$(strlen "$tag_content")
 
 run_tests 'tag' $tag_sha1 $tag_size "$tag_content" "$tag_content"
 
-test_expect_success \
-    "Reach a blob from a tag pointing to it" \
-    "test '$hello_content' = \"\$(git cat-file blob $tag_sha1)\""
+test_expect_success "Reach a blob from a tag pointing to it" '
+	echo_without_newline "$hello_content" >expect &&
+	git cat-file blob $tag_sha1 >actual &&
+	test_cmp expect actual
+'
 
 for batch in batch batch-check batch-command
 do
@@ -334,30 +336,47 @@ do
 done
 
 test_expect_success "--batch-check for a non-existent named object" '
-    test "foobar42 missing
-foobar84 missing" = \
-    "$( ( echo foobar42 && echo_without_newline foobar84 ) | git cat-file --batch-check)"
+	cat >expect <<-EOF &&
+	foobar42 missing
+	foobar84 missing
+	EOF
+
+	printf "foobar42\nfoobar84" >in &&
+	git cat-file --batch-check <in >actual &&
+	test_cmp expect actual
 '
 
 test_expect_success "--batch-check for a non-existent hash" '
-    test "0000000000000000000000000000000000000042 missing
-0000000000000000000000000000000000000084 missing" = \
-    "$( ( echo 0000000000000000000000000000000000000042 &&
-	 echo_without_newline 0000000000000000000000000000000000000084 ) |
-       git cat-file --batch-check)"
+	cat >expect <<-EOF &&
+	0000000000000000000000000000000000000042 missing
+	0000000000000000000000000000000000000084 missing
+	EOF
+
+	printf "0000000000000000000000000000000000000042\n0000000000000000000000000000000000000084" >in &&
+	git cat-file --batch-check <in >actual &&
+	test_cmp expect actual
 '
 
 test_expect_success "--batch for an existent and a non-existent hash" '
-    test "$tag_sha1 tag $tag_size
-$tag_content
-0000000000000000000000000000000000000000 missing" = \
-    "$( ( echo $tag_sha1 &&
-	 echo_without_newline 0000000000000000000000000000000000000000 ) |
-       git cat-file --batch)"
+	cat >expect <<-EOF &&
+	$tag_sha1 tag $tag_size
+	$tag_content
+	0000000000000000000000000000000000000000 missing
+	EOF
+
+	printf "$tag_sha1\n0000000000000000000000000000000000000000" >in &&
+	git cat-file --batch <in >actual &&
+	test_cmp expect actual
 '
 
 test_expect_success "--batch-check for an empty line" '
-    test " missing" = "$(echo | git cat-file --batch-check)"
+	cat >expect <<-EOF &&
+	 missing
+	EOF
+
+	echo >in &&
+	git cat-file --batch-check <in >actual &&
+	test_cmp expect actual
 '
 
 test_expect_success 'empty --batch-check notices missing object' '
@@ -384,7 +403,8 @@ deadbeef missing
 
 test_expect_success '--batch with multiple sha1s gives correct format' '
 	echo "$batch_output" >expect &&
-	echo_without_newline "$batch_input" | git cat-file --batch >actual &&
+	echo_without_newline "$batch_input" >in &&
+	git cat-file --batch <in >actual &&
 	test_cmp expect actual
 '
 
@@ -411,13 +431,17 @@ deadbeef missing
  missing"
 
 test_expect_success "--batch-check with multiple sha1s gives correct format" '
-    test "$batch_check_output" = \
-    "$(echo_without_newline "$batch_check_input" | git cat-file --batch-check)"
+	echo "$batch_check_output" >expect &&
+	echo_without_newline "$batch_check_input" >in &&
+	git cat-file --batch-check <in >actual &&
+	test_cmp expect actual
 '
 
 test_expect_success "--batch-check, -z with multiple sha1s gives correct format" '
-    echo_without_newline_nul "$batch_check_input" >in &&
-    test "$batch_check_output" = "$(git cat-file --batch-check -z <in)"
+	echo "$batch_check_output" >expect &&
+	echo_without_newline_nul "$batch_check_input" >in &&
+	git cat-file --batch-check -z <in >actual &&
+	test_cmp expect actual
 '
 
 test_expect_success FUNNYNAMES '--batch-check, -z with newline in input' '