Fix String::Trim and add test

test/tests/StringTest.cpp

@@ -0,0 +1,27 @@
+#include <string>
+#include <tuple>
+#include <gtest/gtest.h>
+#include <openrct2/core/String.hpp>
+
+using TCase = std::tuple<std::string, std::string>;
+
+class StringTest : public testing::TestWithParam<TCase>
+{
+};
+
+INSTANTIATE_TEST_CASE_P(TrimData, StringTest, testing::Values(
+    TCase("string", "string"),
+    TCase("  string", "string"),
+    TCase("string  ", "string"),
+    TCase("   some   string  ", "some   string"),
+    TCase("      ", ""),
+    TCase("", "")
+));
+TEST_P(StringTest, Trim)
+{
+    auto testCase = GetParam();
+    std::string input = std::get<0>(testCase);
+    std::string expected = std::get<1>(testCase);
+    std::string actual = String::Trim(input);
+    ASSERT_EQ(expected, actual);
+}