t/40-commit: Extract assert_branch function and abbreviate commits

All calls to git-show-ref now set --abbrev=12 to make things a bit
more short and sweet. If this fails under earlier versions of Git
that we need to support with tests, we'll have to back this out,
but it's been tested on 2.11.0 and 1.9.1.

The new assert_branch function in most cases takes the just the
git-show-ref output, but you can give it a branch name if you need to
get information for a branch other than the default $branch we put our
test commits on.

t/40-commit.t

@@ -11,7 +11,12 @@ export GIT_AUTHOR_DATE=2000-01-01T00:00:00
 export GIT_COMMITTER_DATE=2001-01-01T00:00:00
 
 git="git --git-dir=$repo/.git --work-tree=$repo"
-git_show_refs="$git show-ref"
+git_show_refs="$git show-ref --abbrev=12"
+assert_branch() {
+    local output="$1"
+    local pattern="${2:-$branch}"
+    test_equal "$output" "$($git_show_refs "$pattern")"
+}
 
 make_test_repo() {
     rm -rf tmp/test
@@ -77,16 +82,13 @@ start_test 'Commit data correct'
 
 make_test_repo
 $git branch $branch
-test_equal "737b0f4390513917f3a19eece0dcd6a04e5deca3 refs/heads/master
-737b0f4390513917f3a19eece0dcd6a04e5deca3 refs/heads/testbr" \
-            "$($git_show_refs)"
+assert_branch '737b0f439051 refs/heads/master' master
+assert_branch '737b0f439051 refs/heads/testbr'
 
 echo bar > $files/one
 echo bar > $files/subdir/two
 $git commit-filetree $branch $files
-
-test_equal "003e5987f3852ef5ad25ebd23b968de5f5104550 refs/heads/testbr" \
-            "$($git_show_refs $branch)"
+assert_branch '003e5987f385 refs/heads/testbr'
 
 end_test
 
@@ -100,9 +102,7 @@ $git branch $branch
 echo bar > $files/one
 echo bar > $files/subdir/two
 $git commit-filetree refs/heads/$branch $files
-
-test_equal "003e5987f3852ef5ad25ebd23b968de5f5104550 refs/heads/testbr" \
-            "$($git_show_refs $branch)"
+assert_branch '003e5987f385 refs/heads/testbr'
 
 end_test
 
@@ -116,9 +116,7 @@ $git branch $branch
 echo bar > $files/one
 echo bar > $files/subdir/two
 (cd $repo && ../../../bin/git-commit-filetree $branch ../files)
-
-test_equal "003e5987f3852ef5ad25ebd23b968de5f5104550 refs/heads/testbr" \
-            "$($git_show_refs $branch)"
+assert_branch '003e5987f385 refs/heads/testbr'
 
 end_test
 
@@ -132,8 +130,7 @@ echo bar > $files/subdir/two
 $git commit-filetree $branch $files
 $git commit-filetree $branch $files
 $git commit-filetree $branch $files
-test_equal "003e5987f3852ef5ad25ebd23b968de5f5104550 refs/heads/testbr" \
-            "$($git_show_refs $branch)"
+assert_branch '003e5987f385 refs/heads/testbr'
 end_test
 
 ##### 9