t3404: abstract away SHA-1-specific constants

Adjust the test so that it computes variables for object IDs instead of
using hard-coded hashes.  Add a use of $EMPTY_TREE instead of a
hard-coded value.  Remove a comment about hard-coded hashes which is no
longer applicable.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3404-rebase-interactive.sh

@@ -29,9 +29,6 @@ Initial setup:
 
 . "$TEST_DIRECTORY"/lib-rebase.sh
 
-# WARNING: Modifications to the initial repository can change the SHA ID used
-# in the expect2 file for the 'stop on conflicting pick' test.
-
 test_expect_success 'setup' '
 	test_commit A file1 &&
 	test_commit B file1 &&
@@ -233,25 +230,28 @@ test_expect_success 'exchange two commits' '
 	set_fake_editor &&
 	FAKE_LINES="2 1" git rebase -i HEAD~2 &&
 	test H = $(git cat-file commit HEAD^ | sed -ne \$p) &&
-	test G = $(git cat-file commit HEAD | sed -ne \$p)
+	test G = $(git cat-file commit HEAD | sed -ne \$p) &&
+	blob1=$(git rev-parse --short HEAD^:file1) &&
+	blob2=$(git rev-parse --short HEAD:file1) &&
+	commit=$(git rev-parse --short HEAD)
 '
 
 test_expect_success 'stop on conflicting pick' '
-	cat >expect <<-\EOF &&
+	cat >expect <<-EOF &&
 	diff --git a/file1 b/file1
-	index f70f10e..fd79235 100644
+	index $blob1..$blob2 100644
 	--- a/file1
 	+++ b/file1
 	@@ -1 +1 @@
 	-A
 	+G
 	EOF
-	cat >expect2 <<-\EOF &&
+	cat >expect2 <<-EOF &&
 	<<<<<<< HEAD
 	D
 	=======
 	G
-	>>>>>>> 5d18e54... G
+	>>>>>>> $commit... G
 	EOF
 	git tag new-branch1 &&
 	set_fake_editor &&
@@ -1003,7 +1003,7 @@ test_expect_success 'rebase -i --root temporary sentinel commit' '
 	git checkout B &&
 	set_fake_editor &&
 	test_must_fail env FAKE_LINES="2" git rebase -i --root &&
-	git cat-file commit HEAD | grep "^tree 4b825dc642cb" &&
+	git cat-file commit HEAD | grep "^tree $EMPTY_TREE" &&
 	git rebase --abort
 '
 
@@ -1161,7 +1161,7 @@ test_expect_success 'rebase -i error on commits with \ in message' '
 	test_expect_code 1 grep  "	emp" error
 '
 
-test_expect_success 'short SHA-1 setup' '
+test_expect_success SHA1 'short SHA-1 setup' '
 	test_when_finished "git checkout master" &&
 	git checkout --orphan collide &&
 	git rm -rf . &&
@@ -1173,7 +1173,7 @@ test_expect_success 'short SHA-1 setup' '
 	)
 '
 
-test_expect_success 'short SHA-1 collide' '
+test_expect_success SHA1 'short SHA-1 collide' '
 	test_when_finished "reset_rebase && git checkout master" &&
 	git checkout collide &&
 	(