test(ui): Add test_validation_result.cpp

Split from monolithic test_parameter_validation.cpp into focused
ValidationResult tests covering:
- Single and multiple error formatting
- Empty error list (valid result) behavior
- Summary generation with validated parameters
- Parameter count reporting in summaries

Tests the ValidationResult data structure and its user-facing
output methods (format_errors, format_summary). Validates that
error messages and validation summaries are clear and informative
for end users.

Completes UI parameter validation test refactoring into three
focused test files for better maintainability.

Author: ahojukka5

tests/unit/ui/test_validation_result.cpp

@@ -0,0 +1,57 @@
+// SPDX-FileCopyrightText: 2025 VTT Technical Research Centre of Finland Ltd
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+#include "openpfc/ui/parameter_validator.hpp"
+#include <catch2/catch_all.hpp>
+
+using namespace pfc::ui;
+
+TEST_CASE("ValidationResult error formatting", "[validation_result][unit]") {
+  ValidationResult result;
+
+  SECTION("Single error") {
+    result.errors.push_back("temperature: Value below minimum (0)");
+    result.valid = false;
+    REQUIRE_FALSE(result.is_valid());
+
+    std::string errors = result.format_errors();
+    REQUIRE(errors.find("temperature") != std::string::npos);
+    REQUIRE(errors.find("below minimum") != std::string::npos);
+  }
+
+  SECTION("Multiple errors") {
+    result.errors.push_back("temperature: Value below minimum");
+    result.errors.push_back("mobility: Value exceeds maximum");
+    result.valid = false;
+    REQUIRE_FALSE(result.is_valid());
+
+    std::string errors = result.format_errors();
+    REQUIRE(errors.find("temperature") != std::string::npos);
+    REQUIRE(errors.find("mobility") != std::string::npos);
+  }
+
+  SECTION("No errors") {
+    REQUIRE(result.is_valid());
+    std::string errors = result.format_errors();
+    REQUIRE(errors.find("No errors") != std::string::npos);
+  }
+}
+
+TEST_CASE("ValidationResult summary", "[validation_result][unit]") {
+  ValidationResult result;
+
+  SECTION("Valid result summary") {
+    std::string summary = result.format_summary();
+    REQUIRE(summary.find("Validation Summary") != std::string::npos);
+  }
+
+  SECTION("With validated parameters") {
+    result.validated_params["temperature"] = "3300.0";
+    result.validated_params["mobility"] = "50.0";
+
+    std::string summary = result.format_summary();
+    REQUIRE(summary.find("2 parameter") != std::string::npos);
+    REQUIRE(summary.find("temperature") != std::string::npos);
+    REQUIRE(summary.find("mobility") != std::string::npos);
+  }
+}