test-lib: make test_expect_code a test command

Change test_expect_code to be a normal test command instead of a
top-level command.

As a top-level command it would fail in cases like:

    test_expect_code 1 'phoney' '
        foo && bar && (exit 1)
    '

Here the test might incorrectly succeed if "foo" or "bar" happened to
fail with exit status 1. Instead we now do:

    test_expect_success 'phoney' '
        foo && bar && test_expect_code 1 "(exit 1)"
    '

Which will only succeed if "foo" and "bar" return status 0, and "(exit
1)" returns status 1.  Note that test_expect_code has been made slightly
noisier, as it reports the exit code it receives even upon success.

Some test code in t0000-basic.sh relied on the old semantics of
test_expect_code to test the test_when_finished command. I've
converted that code to use an external test similar to the TODO test I
added in v1.7.3-rc0~2^2~3.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Acked-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 830e5e7..d86edcd 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -473,24 +473,6 @@
 	echo >&3 ""
 }
 
-test_expect_code () {
-	test "$#" = 4 && { prereq=$1; shift; } || prereq=
-	test "$#" = 3 ||
-	error "bug in the test script: not 3 or 4 parameters to test-expect-code"
-	if ! test_skip "$@"
-	then
-		say >&3 "expecting exit code $1: $3"
-		test_run_ "$3"
-		if [ "$?" = 0 -a "$eval_ret" = "$1" ]
-		then
-			test_ok_ "$2"
-		else
-			test_failure_ "$@"
-		fi
-	fi
-	echo >&3 ""
-}
-
 # test_external runs external test scripts that provide continuous
 # test output about their progress, and succeeds/fails on
 # zero/non-zero exit code.  It outputs the test output on stdout even
@@ -658,6 +640,28 @@
 	return 0
 }
 
+# Similar to test_must_fail and test_might_fail, but check that a
+# given command exited with a given exit code. Meant to be used as:
+#
+#	test_expect_success 'Merge with d/f conflicts' '
+#		test_expect_code 1 git merge "merge msg" B master
+#	'
+
+test_expect_code () {
+	want_code=$1
+	shift
+	"$@"
+	exit_code=$?
+	if test $exit_code = $want_code
+	then
+		echo >&2 "test_expect_code: command exited with $exit_code: $*"
+		return 0
+	else
+		echo >&2 "test_expect_code: command exited with $exit_code, we wanted $want_code $*"
+		return 1
+	fi
+}
+
 # test_cmp is a helper function to compare actual and expected output.
 # You can use it like:
 #