Rewrite the client code a bit and give each response object its own file

Author: prep

balance.go

@@ -0,0 +1,8 @@
+package messagebird
+
+type Balance struct {
+	Payment string
+	Type    string
+	Amount  int
+	Errors  []Error
+}

balance_test.go

@@ -0,0 +1,49 @@
+package messagebird
+
+import "testing"
+
+var balanceObject []byte = []byte(`{
+  "payment":"prepaid",
+  "type":"credits",
+  "amount":9
+}`)
+
+func TestBalance(t *testing.T) {
+	SetServerResponse(200, balanceObject)
+
+	balance, err := mbClient.Balance()
+	if err != nil {
+		t.Fatalf("Didn't expect error while fetching the balance: %s", err)
+	}
+
+	if balance.Payment != "prepaid" {
+		t.Errorf("Unexpected balance payment: %s", balance.Payment)
+	}
+	if balance.Type != "credits" {
+		t.Errorf("Unexpected balance type: %s", balance.Type)
+	}
+	if balance.Amount != 9 {
+		t.Errorf("Unexpected balance amount: %d", balance.Amount)
+	}
+}
+
+func TestBalanceError(t *testing.T) {
+	SetServerResponse(405, accessKeyErrorObject)
+
+	balance, err := mbClient.Balance()
+	if err != ErrResponse {
+		t.Fatalf("Expected ErrResponse to be returned, instead I got %s", err)
+	}
+
+	if len(balance.Errors) != 1 {
+		t.Fatalf("Unexpected number of errors: %d", len(balance.Errors))
+	}
+
+	if balance.Errors[0].Code != 2 {
+		t.Errorf("Unexpected error code: %d", balance.Errors[0].Code)
+	}
+
+	if balance.Errors[0].Parameter != "access_key" {
+		t.Errorf("Unexpected error parameter: %s", balance.Errors[0].Parameter)
+	}
+}