Add troll_shield_test.go with simple test for getUserName

The other functions is just too hard to mocking properly. I need
to refactor it later to make easier to test.

Currently, the most critical function that needs test it is
findTrollHouses.

troll_shield_test.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"testing"
+
+	tgbotapi "github.com/go-telegram-bot-api/telegram-bot-api"
+)
+
+func TestGetUserName(t *testing.T) {
+	user1 := tgbotapi.User{
+		FirstName: "Rolisvaldo",
+	}
+	if got := getUserName(user1); got != "Rolisvaldo" {
+		t.Errorf("getUserName when only FirstName is available should return it, not %v", got)
+	}
+
+	user2 := tgbotapi.User{
+		FirstName: "Rolisvaldo",
+		LastName:  "Da Silva",
+	}
+	if got := getUserName(user2); got != "Rolisvaldo Da Silva" {
+		t.Errorf("getUserName when FirstName and LastName are available should return it, not %v", got)
+	}
+
+	user3 := tgbotapi.User{
+		FirstName: "Rolisvaldo",
+		LastName:  "Da Silva",
+		UserName:  "rolisvaldo",
+	}
+	if got := getUserName(user3); got != "@rolisvaldo" {
+		t.Errorf("getUserName when only UserName is available should return it with @, not %v", got)
+	}
+}