Define project-wide GIT setup for all tests

Disabling system/global git configs and setting default project-wide GIT
configuration for the duration of running tests. Temporary GIT
configuration is set inside git-subrepo project-top-dir.
Also, initialize own git repo, if project isn't a git clone and ensure
that the project is not in a GIT detached HEAD state.

Author: spog

test/00-git-config.t

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+
+set -e
+
+source test/setup
+
+use Test::More
+
+note "Define project-wide GIT setup for all tests"
+
+# Get git-subrepo project top directory
+PROJ_DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )/.." && pwd )
+
+if [ -z "${PROJ_DIR}" ] || [ "${HOME}" != "${PROJ_DIR}" ]; then
+  is "${HOME}" "${PROJ_DIR}" \
+  "To define project-wide GIT setup for all tests: HOME '${HOME}' should equal PROJ_DIR '${PROJ_DIR}'"
+else
+
+  # Real GIT configuration for tests is set here:
+  rm -f "${PROJ_DIR}/.gitconfig"
+  git config --global user.email "[email protected]"
+  git config --global user.name "Your Name"
+  git config --global init.defaultBranch "master"
+  git config --global --add safe.directory "${PROJ_DIR}"
+  git config --global --add safe.directory "${PROJ_DIR}/.git"
+  git config --list
+
+  test-exists "${PROJ_DIR}/.gitconfig"
+
+  # Running tests depends on the whole project being git initialized.
+  # So, git initialize the project, if necessary.
+  if [ ! -d "${PROJ_DIR}/.git" ]; then
+    cd "${PROJ_DIR}"
+    git init .
+    git add .
+    git commit -a -m"Initial commit"
+    cd -
+  fi
+
+  test-exists "${PROJ_DIR}/.git/"
+
+  # Running tests depends on the whole project not being in a GIT detached HEAD state.
+  if ! git symbolic-ref --short --quiet HEAD &> /dev/null; then
+    git checkout -b test
+  fi
+
+  ok "$(
+    git symbolic-ref --short --quiet HEAD &> /dev/null
+  )" "Whole project is not in a GIT detached HEAD state"
+
+fi
+
+done_testing
+
+teardown

test/setup

@@ -15,9 +15,15 @@ if [ ! -d "${SCRIPT_DIR}/../.git" ]; then
 	git config user.name "YouUser"
 	git add .
 	git commit -a -m"Initial commit"
-	git config --list
 fi
 
+# Disable any GIT configuration set outside this 'git-subrepo' project.
+# Real GIT configuration for tests is set through the first test
+# (00-git-config.t).
+export XDG_CONFIG_HOME=$PWD
+export HOME=$PWD
+export GIT_CONFIG_NOSYSTEM=1
+
 # Generate additional testing git repos, if not already present.
 mkdir -p  "${SCRIPT_DIR}/repo"
 if [ ! -d "${SCRIPT_DIR}/repo/bar" ]; then