Added vsnprintf test.

tests/vsnprintf_test.cpp

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2010-2017 Branimir Karadzic. All rights reserved.
+ * License: https://github.com/bkaradzic/bx#license-bsd-2-clause
+ */
+
+#include "test.h"
+#include <bx/string.h>
+
+TEST_CASE("vsnprintf NULL buffer", "No output buffer provided.")
+{
+	REQUIRE(4 == bx::snprintf(NULL, 0, "test") );
+
+	REQUIRE(1 == bx::snprintf(NULL, 0, "%d", 1) );
+}
+
+TEST_CASE("vsnprintf truncated", "Truncated output buffer.")
+{
+	char buffer[7];
+
+	REQUIRE(10 == bx::snprintf(buffer, BX_COUNTOF(buffer), "Ten chars!") );
+	REQUIRE(0  == strcmp(buffer, "Ten ch") );
+}