Port git submodule test from next.

test/segments/vcs-git.spec

@@ -503,4 +503,33 @@ function testBranchNameScriptingVulnerability() {
   assertEquals '%K{002} %F{000} $(./evil_script.sh) %k%F{002}%f ' "$(build_left_prompt)"
 }
 
+function testGitSubmoduleWorks() {
+  local -a POWERLEVEL9K_LEFT_PROMPT_ELEMENTS
+  POWERLEVEL9K_LEFT_PROMPT_ELEMENTS=(vcs)
+  local POWERLEVEL9K_VCS_SHOW_SUBMODULE_DIRTY="true"
+  unset POWERLEVEL9K_VCS_UNTRACKED_BACKGROUND
+
+  mkdir ../submodule
+  cd ../submodule
+  git init 1>/dev/null
+  touch "i-am-tracked.txt"
+  git add . 1>/dev/null && git commit -m "Initial Commit" 1>/dev/null
+
+  local submodulePath="${PWD}"
+
+  cd -
+  git submodule add "${submodulePath}" 2>/dev/null
+  git commit -m "Add submodule" 1>/dev/null
+
+  cd submodule
+
+  source "${P9K_HOME}/powerlevel9k.zsh-theme"
+
+  local result="$(build_left_prompt)"
+  [[ "$result" =~ ".*(is outside repository)+" ]] && return 1
+
+  assertEquals "%K{002} %F{000} master %k%F{002}%f " "$result"
+}
+
+
 source shunit2/shunit2