test: add tests for handler, email, cmd/server, version and enforce 80% coverage

internal/config/config_test.go

@@ -95,3 +95,16 @@ to = "you@example.com"
 		t.Fatal("expected an error for an unknown field")
 	}
 }
+
+func TestConfigPath(t *testing.T) {
+	if got := ConfigPath(); got != "/etc/nuntius/config.toml" {
+		t.Errorf("ConfigPath() = %q, want %q", got, "/etc/nuntius/config.toml")
+	}
+}
+
+func TestSMTPConfigAddrFor(t *testing.T) {
+	smtp := SMTPConfig{Host: "smtp.example.com", Port: 587}
+	if got := smtp.AddrFor(); got != "smtp.example.com:587" {
+		t.Errorf("AddrFor() = %q, want %q", got, "smtp.example.com:587")
+	}
+}