fix regex and actually test the check function

packer/core.go

@@ -350,7 +350,7 @@ func (c *Core) validate() error {
 func isDoneInterpolating(v string) (bool, error) {
 	// Check for whether the var contains any more references to `user`, wrapped
 	// in interpolation syntax.
-	filter := `{{\s*|user\s*|\x60?.*\x60?}}`
+	filter := `{{\s*user\s*\x60.*\x60\s*}}`
 	matched, err := regexp.MatchString(filter, v)
 	if err != nil {
 		return false, fmt.Errorf("Can't tell if interpolation is done: %s", err)

packer/core_test.go

@@ -679,7 +679,7 @@ func TestSensitiveVars(t *testing.T) {
 }
 
 // Normally I wouldn't test a little helper function, but it's regex.
-func testisDoneInterpolating(t *testing.T) {
+func TestIsDoneInterpolating(t *testing.T) {
 	cases := []struct {
 		inputString  string
 		expectedBool bool