+#
+# case #18
+#
+############################################################
+#
+# Input:
+#
+# - GIT_WORK_TREE is not set
+# - GIT_DIR is set
+# - core.worktree is not set
+# - .git is a directory
+# - core.bare is set
+#
+# Output:
+#
+# - no worktree (rule #8)
+# - cwd is unchanged
+# - prefix is NULL
+# - git_dir is set to $GIT_DIR
+# - cwd can't be outside worktree
+
+test_expect_success '#18: setup' '
+ unset GIT_DIR GIT_WORK_TREE &&
+ mkdir 18 18/sub &&
+ cd 18 &&
+ git init &&
+ mkdir .git/wt .git/wt/sub &&
+ git config core.bare true &&
+ cd ..
+'
+
+test_expect_success '#18: (rel) at root' '
+ cat >18/expected <<EOF &&
+setup: git_dir: .git
+setup: worktree: (null)
+setup: cwd: $TRASH_DIRECTORY/18
+setup: prefix: (null)
+EOF
+ test_repo 18 .git
+'
+
+test_expect_success '#18: at root' '
+ cat >18/expected <<EOF &&
+setup: git_dir: $TRASH_DIRECTORY/18/.git
+setup: worktree: (null)
+setup: cwd: $TRASH_DIRECTORY/18
+setup: prefix: (null)
+EOF
+ test_repo 18 "$TRASH_DIRECTORY/18/.git"
+'
+
+test_expect_success '#18: (rel) in subdir' '
+ cat >18/sub/expected <<EOF &&
+setup: git_dir: ../.git
+setup: worktree: (null)
+setup: cwd: $TRASH_DIRECTORY/18/sub
+setup: prefix: (null)
+EOF
+ test_repo 18/sub ../.git
+'
+
+test_expect_success '#18: in subdir' '
+ cat >18/sub/expected <<EOF &&
+setup: git_dir: $TRASH_DIRECTORY/18/.git
+setup: worktree: (null)
+setup: cwd: $TRASH_DIRECTORY/18/sub
+setup: prefix: (null)
+EOF
+ test_repo 18/sub "$TRASH_DIRECTORY/18/.git"
+'
+