tests: document cherry-pick behavior in face of conflicts

We are about to change the format of the conflict hunks that
cherry-pick and revert write.  Add tests checking the current behavior
first.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3507-cherry-pick-conflict.sh

@@ -0,0 +1,198 @@
+#!/bin/sh
+
+test_description='test cherry-pick and revert with conflicts
+
+  -
+  + picked: rewrites foo to c
+  + base: rewrites foo to b
+  + initial: writes foo as a, unrelated as unrelated
+
+'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+
+	echo unrelated >unrelated &&
+	git add unrelated &&
+	test_commit initial foo a &&
+	test_commit base foo b &&
+	test_commit picked foo c &&
+	git config advice.detachedhead false
+
+'
+
+test_expect_success 'failed cherry-pick does not advance HEAD' '
+
+	git checkout -f initial^0 &&
+	git read-tree -u --reset HEAD &&
+	git clean -d -f -f -q -x &&
+
+	git update-index --refresh &&
+	git diff-index --exit-code HEAD &&
+
+	head=$(git rev-parse HEAD) &&
+	test_must_fail git cherry-pick picked &&
+	newhead=$(git rev-parse HEAD) &&
+
+	test "$head" = "$newhead"
+'
+
+test_expect_success 'failed cherry-pick produces dirty index' '
+
+	git checkout -f initial^0 &&
+	git read-tree -u --reset HEAD &&
+	git clean -d -f -f -q -x &&
+
+	git update-index --refresh &&
+	git diff-index --exit-code HEAD &&
+
+	test_must_fail git cherry-pick picked &&
+
+	test_must_fail git update-index --refresh -q &&
+	test_must_fail git diff-index --exit-code HEAD
+'
+
+test_expect_success 'failed cherry-pick registers participants in index' '
+
+	git read-tree -u --reset HEAD &&
+	git clean -d -f -f -q -x &&
+	{
+		git checkout base -- foo &&
+		git ls-files --stage foo &&
+		git checkout initial -- foo &&
+		git ls-files --stage foo &&
+		git checkout picked -- foo &&
+		git ls-files --stage foo
+	} > stages &&
+	sed "
+		1 s/ 0	/ 1	/
+		2 s/ 0	/ 2	/
+		3 s/ 0	/ 3	/
+	" < stages > expected &&
+	git checkout -f initial^0 &&
+
+	git update-index --refresh &&
+	git diff-index --exit-code HEAD &&
+
+	test_must_fail git cherry-pick picked &&
+	git ls-files --stage --unmerged > actual &&
+
+	test_cmp expected actual
+'
+
+test_expect_success 'failed cherry-pick describes conflict in work tree' '
+
+	git checkout -f initial^0 &&
+	git read-tree -u --reset HEAD &&
+	git clean -d -f -f -q -x &&
+	cat <<-EOF > expected &&
+	<<<<<<< HEAD
+	a
+	=======
+	c
+	>>>>>>> objid picked
+	EOF
+
+	git update-index --refresh &&
+	git diff-index --exit-code HEAD &&
+
+	test_must_fail git cherry-pick picked &&
+
+	sed "s/[a-f0-9]*\.\.\./objid/" foo > actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'diff3 -m style' '
+
+	git config merge.conflictstyle diff3 &&
+	git checkout -f initial^0 &&
+	git read-tree -u --reset HEAD &&
+	git clean -d -f -f -q -x &&
+	cat <<-EOF > expected &&
+	<<<<<<< HEAD
+	a
+	|||||||
+	b
+	=======
+	c
+	>>>>>>> objid picked
+	EOF
+
+	git update-index --refresh &&
+	git diff-index --exit-code HEAD &&
+
+	test_must_fail git cherry-pick picked &&
+
+	sed "s/[a-f0-9]*\.\.\./objid/" foo > actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'revert also handles conflicts sanely' '
+
+	git config --unset merge.conflictstyle &&
+	git read-tree -u --reset HEAD &&
+	git clean -d -f -f -q -x &&
+	cat <<-EOF > expected &&
+	<<<<<<< HEAD
+	a
+	=======
+	b
+	>>>>>>> objid picked
+	EOF
+	{
+		git checkout picked -- foo &&
+		git ls-files --stage foo &&
+		git checkout initial -- foo &&
+		git ls-files --stage foo &&
+		git checkout base -- foo &&
+		git ls-files --stage foo
+	} > stages &&
+	sed "
+		1 s/ 0	/ 1	/
+		2 s/ 0	/ 2	/
+		3 s/ 0	/ 3	/
+	" < stages > expected-stages &&
+	git checkout -f initial^0 &&
+
+	git update-index --refresh &&
+	git diff-index --exit-code HEAD &&
+
+	head=$(git rev-parse HEAD) &&
+	test_must_fail git revert picked &&
+	newhead=$(git rev-parse HEAD) &&
+	git ls-files --stage --unmerged > actual-stages &&
+
+	test "$head" = "$newhead" &&
+	test_must_fail git update-index --refresh -q &&
+	test_must_fail git diff-index --exit-code HEAD &&
+	test_cmp expected-stages actual-stages &&
+	sed "s/[a-f0-9]*\.\.\./objid/" foo > actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'revert conflict, diff3 -m style' '
+	git config merge.conflictstyle diff3 &&
+	git checkout -f initial^0 &&
+	git read-tree -u --reset HEAD &&
+	git clean -d -f -f -q -x &&
+	cat <<-EOF > expected &&
+	<<<<<<< HEAD
+	a
+	|||||||
+	c
+	=======
+	b
+	>>>>>>> objid picked
+	EOF
+
+	git update-index --refresh &&
+	git diff-index --exit-code HEAD &&
+
+	test_must_fail git revert picked &&
+
+	sed "s/[a-f0-9]*\.\.\./objid/" foo > actual &&
+	test_cmp expected actual
+'
+
+test_done