msvcrt/tests: Add tests for wcsdup.

dlls/msvcrt/tests/string.c

@@ -649,6 +649,15 @@ static void test_strdup(void)
     ok(errno == 0xdeadbeef, "errno is %d, expected 0xdeadbeef\n", errno);
 }
 
+static void test_wcsdup(void)
+{
+    WCHAR *str;
+    errno = 0xdeadbeef;
+    str = wcsdup(0);
+    ok(str == 0, "wcsdup returned %s, expected NULL\n", wine_dbgstr_w(str));
+    ok(errno == 0xdeadbeef, "errno is %d, expected 0xdeadbeef\n", errno);
+}
+
 static void test_strcmp(void)
 {
     int ret = p_strcmp( "abc", "abcd" );
@@ -4705,6 +4714,7 @@ START_TEST(string)
     test_mbsspn();
     test_mbsspnp();
     test_strdup();
+    test_wcsdup();
     test_strcmp();
     test_strcpy_s();
     test_memcpy_s();