merge: test the top-level merge driver

We seem to have tests for specific merge strategy backends
(e.g. recursive), but not much test coverage for the "git merge"
itself.  As I am planning to update the semantics of merging
"FETCH_HEAD" in such a way that these two

    git pull . topic_a topic_b...

vs.

    git fetch . topic_a topic_b...
    git merge FETCH_HEAD

are truly equivalent, let me add a few test cases to cover the
tricky ones.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/t/t3033-merge-toplevel.sh b/t/t3033-merge-toplevel.sh
new file mode 100755 (executable)
index 0000000..9d92d3c
--- /dev/null
+++ b/t/t3033-merge-toplevel.sh
@@ -0,0 +1,136 @@
+#!/bin/sh
+
+test_description='"git merge" top-level frontend'
+
+. ./test-lib.sh
+
+t3033_reset () {
+       git checkout -B master two &&
+       git branch -f left three &&
+       git branch -f right four
+}
+
+test_expect_success setup '
+       test_commit one &&
+       git branch left &&
+       git branch right &&
+       test_commit two &&
+       git checkout left &&
+       test_commit three &&
+       git checkout right &&
+       test_commit four &&
+       git checkout master
+'
+
+# Local branches
+
+test_expect_success 'merge an octopus into void' '
+       t3033_reset &&
+       git checkout --orphan test &&
+       git rm -fr . &&
+       test_must_fail git merge left right &&
+       test_must_fail git rev-parse --verify HEAD &&
+       git diff --quiet &&
+       test_must_fail git rev-parse HEAD
+'
+
+test_expect_success 'merge an octopus, fast-forward (ff)' '
+       t3033_reset &&
+       git reset --hard one &&
+       git merge left right &&
+       # one is ancestor of three (left) and four (right)
+       test_must_fail git rev-parse --verify HEAD^3 &&
+       git rev-parse HEAD^1 HEAD^2 | sort >actual &&
+       git rev-parse three four | sort >expect &&
+       test_cmp expect actual
+'
+
+test_expect_success 'merge octopus, non-fast-forward (ff)' '
+       t3033_reset &&
+       git reset --hard one &&
+       git merge --no-ff left right &&
+       # one is ancestor of three (left) and four (right)
+       test_must_fail git rev-parse --verify HEAD^4 &&
+       git rev-parse HEAD^1 HEAD^2 HEAD^3 | sort >actual &&
+       git rev-parse one three four | sort >expect &&
+       test_cmp expect actual
+'
+
+test_expect_success 'merge octopus, fast-forward (does not ff)' '
+       t3033_reset &&
+       git merge left right &&
+       # two (master) is not an ancestor of three (left) and four (right)
+       test_must_fail git rev-parse --verify HEAD^4 &&
+       git rev-parse HEAD^1 HEAD^2 HEAD^3 | sort >actual &&
+       git rev-parse two three four | sort >expect &&
+       test_cmp expect actual
+'
+
+test_expect_success 'merge octopus, non-fast-forward' '
+       t3033_reset &&
+       git merge --no-ff left right &&
+       test_must_fail git rev-parse --verify HEAD^4 &&
+       git rev-parse HEAD^1 HEAD^2 HEAD^3 | sort >actual &&
+       git rev-parse two three four | sort >expect &&
+       test_cmp expect actual
+'
+
+# The same set with FETCH_HEAD
+
+test_expect_failure 'merge FETCH_HEAD octopus into void' '
+       t3033_reset &&
+       git checkout --orphan test &&
+       git rm -fr . &&
+       git fetch . left right &&
+       test_must_fail git merge FETCH_HEAD &&
+       test_must_fail git rev-parse --verify HEAD &&
+       git diff --quiet &&
+       test_must_fail git rev-parse HEAD
+'
+
+test_expect_failure 'merge FETCH_HEAD octopus fast-forward (ff)' '
+       t3033_reset &&
+       git reset --hard one &&
+       git fetch . left right &&
+       git merge FETCH_HEAD &&
+       # one is ancestor of three (left) and four (right)
+       test_must_fail git rev-parse --verify HEAD^3 &&
+       git rev-parse HEAD^1 HEAD^2 | sort >actual &&
+       git rev-parse three four | sort >expect &&
+       test_cmp expect actual
+'
+
+test_expect_failure 'merge FETCH_HEAD octopus non-fast-forward (ff)' '
+       t3033_reset &&
+       git reset --hard one &&
+       git fetch . left right &&
+       git merge --no-ff FETCH_HEAD &&
+       # one is ancestor of three (left) and four (right)
+       test_must_fail git rev-parse --verify HEAD^4 &&
+       git rev-parse HEAD^1 HEAD^2 HEAD^3 | sort >actual &&
+       git rev-parse one three four | sort >expect &&
+       test_cmp expect actual
+'
+
+test_expect_failure 'merge FETCH_HEAD octopus fast-forward (does not ff)' '
+       t3033_reset &&
+       git fetch . left right &&
+       git merge FETCH_HEAD &&
+       # two (master) is not an ancestor of three (left) and four (right)
+       test_must_fail git rev-parse --verify HEAD^4 &&
+       git rev-parse HEAD^1 HEAD^2 HEAD^3 | sort >actual &&
+       git rev-parse two three four | sort >expect &&
+       test_cmp expect actual
+'
+
+test_expect_failure 'merge FETCH_HEAD octopus non-fast-forward' '
+       t3033_reset &&
+       git fetch . left right &&
+       git merge --no-ff FETCH_HEAD &&
+       test_must_fail git rev-parse --verify HEAD^4 &&
+       git rev-parse HEAD^1 HEAD^2 HEAD^3 | sort >actual &&
+       git rev-parse two three four | sort >expect &&
+       test_cmp expect actual
+'
+
+test_done