t/t3437: remove the dependency of 'expected-message' file from tests

As it is currently implemented, it's too difficult to follow along and
remember the value of "expected-message" from test to test. It also
makes it difficult to extend tests or add new tests in between existing
tests without negatively impacting other tests.

Let's set up "expected-message" to the precise content needed by the
test, so that both the problems go away and also makes easier to run
tests selectively with '--run' or 'GIT_SKIP_TESTS'

Mentored-by: Christian Couder <[email protected]>
Mentored-by: Phillip Wood <[email protected]>
Helped-by: Eric Sunshine <[email protected]>
Signed-off-by: Charvi Mendiratta <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: charvi-077

t/t3437-rebase-fixup-options.sh

@@ -46,8 +46,6 @@ test_expect_success 'setup' '
 	body
 	EOF
 
-	sed "1,2d" message >expected-message &&
-
 	test_commit A A &&
 	test_commit B B &&
 	get_author HEAD >expected-author &&
@@ -134,6 +132,7 @@ test_expect_success 'simple fixup -c works' '
 test_expect_success 'fixup -C removes amend! from message' '
 	test_when_finished "test_might_fail git rebase --abort" &&
 	git checkout --detach A1 &&
+	git log -1 --pretty=format:%b >expected-message &&
 	FAKE_LINES="1 fixup_-C 2" git rebase -i A &&
 	test_cmp_rev HEAD^ A &&
 	test_cmp_rev HEAD^{tree} A1^{tree} &&
@@ -145,13 +144,14 @@ test_expect_success 'fixup -C removes amend! from message' '
 test_expect_success 'fixup -C with conflicts gives correct message' '
 	test_when_finished "test_might_fail git rebase --abort" &&
 	git checkout --detach A1 &&
+	git log -1 --pretty=format:%b >expected-message &&
+	test_write_lines "" "edited" >>expected-message &&
 	test_must_fail env FAKE_LINES="1 fixup_-C 2" git rebase -i conflicts &&
 	git checkout --theirs -- A &&
 	git add A &&
 	FAKE_COMMIT_AMEND=edited git rebase --continue &&
 	test_cmp_rev HEAD^ conflicts &&
 	test_cmp_rev HEAD^{tree} A1^{tree} &&
-	test_write_lines "" edited >>expected-message &&
 	test_commit_message HEAD expected-message &&
 	get_author HEAD >actual-author &&
 	test_cmp expected-author actual-author