test that go_segment prints nothing if GOPATH is not set

test/segments/go_version.spec

@@ -22,6 +22,17 @@ function mockGo() {
   esac
 }
 
+function mockGoEmptyGopath() {
+  case "$1" in
+  'version')
+    echo 'go version go1.5.3 darwin/amd64'
+    ;;
+  'env')
+    echo ""
+    ;;
+  esac
+}
+
 function testGo() {
   alias go=mockGo
   POWERLEVEL9K_LEFT_PROMPT_ELEMENTS=(go_version)
@@ -35,6 +46,18 @@ function testGo() {
   unalias go
 }
 
+function testGoSegmentPrintsNothingIfEmptyGopath() {
+  alias go=mockGoEmptyGopath
+  POWERLEVEL9K_CUSTOM_WORLD='echo world'
+  POWERLEVEL9K_LEFT_PROMPT_ELEMENTS=(custom_world go_version)
+
+  assertEquals "%K{white} %F{black}world %k%F{white}%f " "$(build_left_prompt)"
+
+  unset POWERLEVEL9K_LEFT_PROMPT_ELEMENTS
+  unset POWERLEVEL9K_CUSTOM_WORLD
+
+}
+
 function testGoSegmentPrintsNothingIfNotInGopath() {
   alias go=mockGo
   POWERLEVEL9K_CUSTOM_WORLD='echo world'