t1500: be considerate to future potential tests

The final batch of git-rev-parse tests work against a non-local object
database named repo.git. This is done by renaming .git to repo.git and
pointing GIT_DIR at it, but the name is never restored to .git at the
end of the script, which can be problematic for tests added in the
future. Be more friendly by instead making repo.git a copy of .git.

Furthermore, make it clear that tests in repo.git will be independent
from the results of earlier tests done in .git by initializing repo.git
earlier in the test sequence.

Likewise, bundle remaining preparation (such as directory creation) into
a common setup test consistent with modern practice.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t1500-rev-parse.sh

@@ -37,6 +37,11 @@ test_rev_parse() {
 
 ROOT=$(pwd)
 
+test_expect_success 'setup' '
+	mkdir -p sub/dir work &&
+	cp -R .git repo.git
+'
+
 test_rev_parse toplevel false false true '' .git
 
 cd .git || exit 1
@@ -45,7 +50,6 @@ cd objects || exit 1
 test_rev_parse .git/objects/ false true false '' "$ROOT/.git"
 cd ../.. || exit 1
 
-mkdir -p sub/dir || exit 1
 cd sub/dir || exit 1
 test_rev_parse subdirectory false false true sub/dir/ "$ROOT/.git"
 cd ../.. || exit 1
@@ -56,7 +60,6 @@ test_rev_parse 'core.bare = true' true false false
 git config --unset core.bare
 test_rev_parse 'core.bare undefined' false false true
 
-mkdir work || exit 1
 cd work || exit 1
 GIT_DIR=../.git
 GIT_CONFIG="$(pwd)"/../.git/config
@@ -71,7 +74,6 @@ test_rev_parse 'GIT_DIR=../.git, core.bare = true' true false false ''
 git config --unset core.bare
 test_rev_parse 'GIT_DIR=../.git, core.bare undefined' false false true ''
 
-mv ../.git ../repo.git || exit 1
 GIT_DIR=../repo.git
 GIT_CONFIG="$(pwd)"/../repo.git/config