pull: add t5572 for submodule updates

Test that the pull command updates the work tree as expected (for
submodule changes which don't result in conflicts) when used without
arguments or with the '--ff', '--ff-only' and '--no-ff' flag each. Add
helper functions to reset the branch to be updated to to the current
HEAD so that pull is doing the transition from HEAD to the given branch.

Set KNOWN_FAILURE_NOFF_MERGE_ATTEMPTS_TO_MERGE_REMOVED_SUBMODULE_FILES
and KNOWN_FAILURE_NOFF_MERGE_DOESNT_CREATE_EMPTY_SUBMODULE_DIR to
document that pull has the same --no-ff known failures merge has.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5572-pull-submodule.sh

@@ -0,0 +1,45 @@
+#!/bin/sh
+
+test_description='pull can handle submodules'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-submodule-update.sh
+
+reset_branch_to_HEAD () {
+	git branch -D "$1" &&
+	git checkout -b "$1" HEAD &&
+	git branch --set-upstream-to="origin/$1" "$1"
+}
+
+git_pull () {
+	reset_branch_to_HEAD "$1" &&
+	git pull
+}
+
+# pulls without conflicts
+test_submodule_switch "git_pull"
+
+git_pull_ff () {
+	reset_branch_to_HEAD "$1" &&
+	git pull --ff
+}
+
+test_submodule_switch "git_pull_ff"
+
+git_pull_ff_only () {
+	reset_branch_to_HEAD "$1" &&
+	git pull --ff-only
+}
+
+test_submodule_switch "git_pull_ff_only"
+
+git_pull_noff () {
+	reset_branch_to_HEAD "$1" &&
+	git pull --no-ff
+}
+
+KNOWN_FAILURE_NOFF_MERGE_DOESNT_CREATE_EMPTY_SUBMODULE_DIR=1
+KNOWN_FAILURE_NOFF_MERGE_ATTEMPTS_TO_MERGE_REMOVED_SUBMODULE_FILES=1
+test_submodule_switch "git_pull_noff"
+
+test_done