Add unit test for StringUtil's newly added JoinStrings

Source/UnitTests/Common/CMakeLists.txt

@@ -9,4 +9,5 @@ add_dolphin_test(FixedSizeQueueTest FixedSizeQueueTest.cpp)
 add_dolphin_test(FlagTest FlagTest.cpp)
 add_dolphin_test(MathUtilTest MathUtilTest.cpp)
 add_dolphin_test(NandPathsTest NandPathsTest.cpp)
+add_dolphin_test(StringUtilTest StringUtilTest.cpp)
 add_dolphin_test(x64EmitterTest x64EmitterTest.cpp)

Source/UnitTests/Common/StringUtilTest.cpp

@@ -0,0 +1,18 @@
+// Copyright 2016 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#include <gtest/gtest.h>
+#include <string>
+#include <vector>
+
+#include "Common/StringUtil.h"
+
+TEST(StringUtil, JoinStrings)
+{
+  EXPECT_EQ("", JoinStrings({}, ", "));
+  EXPECT_EQ("a", JoinStrings({"a"}, ","));
+  EXPECT_EQ("ab", JoinStrings({"a", "b"}, ""));
+  EXPECT_EQ("a, bb, c", JoinStrings({"a", "bb", "c"}, ", "));
+  EXPECT_EQ("???", JoinStrings({"?", "?"}, "?"));
+}