t3427: move the filter-branch invocation into the setup case

The step to prepare a pre-rebase commit history is _identical_ in _all_
of the test cases (except of course the `setup` case). It should
therefore clearly a part of the `setup` test case instead.

As the `git filter-branch` command is quite costly on platforms where
Unix shell scripting is simply slow (meaning: on Windows), this shaves
off a noticeable part of the runtime: in this developer's setup, the
time was reduced from ~1m25s to ~1m.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3427-rebase-subtree.sh

@@ -56,16 +56,18 @@ test_expect_success 'setup' '
 
 	: add two extra commits to rebase &&
 	test_commit -C files_subtree master4 &&
-	test_commit files_subtree/master5
+	test_commit files_subtree/master5 &&
+
+	git checkout -b to-rebase &&
+	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
+	git commit -m "Empty commit" --allow-empty
 '
 
 # FAILURE: Does not preserve master4.
 test_expect_failure REBASE_P \
 	'Rebase -Xsubtree --preserve-merges --onto commit 4' '
 	reset_rebase &&
-	git checkout -b rebase-preserve-merges-4 master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
+	git checkout -b rebase-preserve-merges-4 to-rebase &&
 	git rebase -Xsubtree=files_subtree --preserve-merges --onto files-master master &&
 	verbose test "$(commit_message HEAD~)" = "files_subtree/master4"
 '
@@ -74,9 +76,7 @@ test_expect_failure REBASE_P \
 test_expect_failure REBASE_P \
 	'Rebase -Xsubtree --preserve-merges --onto commit 5' '
 	reset_rebase &&
-	git checkout -b rebase-preserve-merges-5 master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
+	git checkout -b rebase-preserve-merges-5 to-rebase &&
 	git rebase -Xsubtree=files_subtree --preserve-merges --onto files-master master &&
 	verbose test "$(commit_message HEAD)" = "files_subtree/master5"
 '
@@ -85,9 +85,7 @@ test_expect_failure REBASE_P \
 test_expect_failure REBASE_P \
 	'Rebase -Xsubtree --keep-empty --preserve-merges --onto commit 4' '
 	reset_rebase &&
-	git checkout -b rebase-keep-empty-4 master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
+	git checkout -b rebase-keep-empty-4 to-rebase &&
 	git rebase -Xsubtree=files_subtree --keep-empty --preserve-merges --onto files-master master &&
 	verbose test "$(commit_message HEAD~2)" = "files_subtree/master4"
 '
@@ -96,9 +94,7 @@ test_expect_failure REBASE_P \
 test_expect_failure REBASE_P \
 	'Rebase -Xsubtree --keep-empty --preserve-merges --onto commit 5' '
 	reset_rebase &&
-	git checkout -b rebase-keep-empty-5 master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
+	git checkout -b rebase-keep-empty-5 to-rebase &&
 	git rebase -Xsubtree=files_subtree --keep-empty --preserve-merges --onto files-master master &&
 	verbose test "$(commit_message HEAD~)" = "files_subtree/master5"
 '
@@ -107,38 +103,30 @@ test_expect_failure REBASE_P \
 test_expect_failure REBASE_P \
 	'Rebase -Xsubtree --keep-empty --preserve-merges --onto empty commit' '
 	reset_rebase &&
-	git checkout -b rebase-keep-empty-empty master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
+	git checkout -b rebase-keep-empty-empty to-rebase &&
 	git rebase -Xsubtree=files_subtree --keep-empty --preserve-merges --onto files-master master &&
 	verbose test "$(commit_message HEAD)" = "Empty commit"
 '
 
 # FAILURE: fatal: Could not parse object
 test_expect_failure 'Rebase -Xsubtree --onto commit 4' '
 	reset_rebase &&
-	git checkout -b rebase-onto-4 master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
+	git checkout -b rebase-onto-4 to-rebase &&
 	git rebase -Xsubtree=files_subtree --onto files-master master &&
 	verbose test "$(commit_message HEAD~2)" = "files_subtree/master4"
 '
 
 # FAILURE: fatal: Could not parse object
 test_expect_failure 'Rebase -Xsubtree --onto commit 5' '
 	reset_rebase &&
-	git checkout -b rebase-onto-5 master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
+	git checkout -b rebase-onto-5 to-rebase &&
 	git rebase -Xsubtree=files_subtree --onto files-master master &&
 	verbose test "$(commit_message HEAD~)" = "files_subtree/master5"
 '
 # FAILURE: fatal: Could not parse object
 test_expect_failure 'Rebase -Xsubtree --onto empty commit' '
 	reset_rebase &&
-	git checkout -b rebase-onto-empty master &&
-	git filter-branch --prune-empty -f --subdirectory-filter files_subtree &&
-	git commit -m "Empty commit" --allow-empty &&
+	git checkout -b rebase-onto-empty to-rebase &&
 	git rebase -Xsubtree=files_subtree --onto files-master master &&
 	verbose test "$(commit_message HEAD)" = "Empty commit"
 '