Adds a test for the birthday filename

model/birthdays_test.go

@@ -42,3 +42,16 @@ func TestNewBirthdayFromRecord(t *testing.T) {
 		}
 	})
 }
+
+func TestFilename(t *testing.T) {
+	birthday := &Birthday{
+		Name:         "John Doe",
+		Email:        "john@doe.com",
+		Phone:        "123456789",
+		YearOfBirth:  2022,
+		MonthOfBirth: 4,
+		DayOfBirth:   6,
+	}
+
+	require.Equal(t, "2022_4_6_123456789.png", birthday.Filename())
+}