Index: rostests/apitests/shlwapi/CMakeLists.txt
===================================================================
--- rostests/apitests/shlwapi/CMakeLists.txt	(revision 73545)
+++ rostests/apitests/shlwapi/CMakeLists.txt	(working copy)
@@ -4,6 +4,7 @@
     PathIsUNCServer.c
     PathIsUNCServerShare.c
     PathUnExpandEnvStrings.c
+    StrFormatByteSizeW.c
     testlist.c)
 
 add_executable(shlwapi_apitest ${SOURCE})
Index: rostests/apitests/shlwapi/StrFormatByteSizeW.c
===================================================================
--- rostests/apitests/shlwapi/StrFormatByteSizeW.c	(nonexistent)
+++ rostests/apitests/shlwapi/StrFormatByteSizeW.c	(working copy)
@@ -0,0 +1,85 @@
+/*
+ * Copyright 2017 Doug Lyons
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
+ */
+
+/* Documentation: https://msdn.microsoft.com/en-us/library/windows/desktop/bb759975(v=vs.85).aspx */
+
+#include <apitest.h>
+#include <shlwapi.h>
+#include <strsafe.h>
+
+#define DO_TEST(exp, str) \
+do { \
+     StrFormatByteSizeW(exp, lpszDest, cchMax);\
+     if (lpszDest[1]==44) lpszDest[1]=46;\
+     ok(_wcsicmp(lpszDest, (str)) == 0, "Expected %s got %s\n",\
+           wine_dbgstr_w((str)), wine_dbgstr_w((lpszDest)));\
+} while (0)
+
+//     lpszDest[1]=L"A";
+//     ok(0,"%d\n",lpszDest[1]);
+
+WCHAR lpszDest[260];
+UINT cchMax=260;
+char* Location;
+
+START_TEST(StrFormatByteSizeW)
+{
+   DO_TEST(0, L"0 bytes");                            // 0x0
+   DO_TEST(1, L"1 bytes");                            // 0x1
+   DO_TEST(1024, L"1.00 KB");                         // 0x400
+   DO_TEST(1048576, L"1.00 MB");                      // 0x100000
+   DO_TEST(1073741824, L"1.00 GB");                   // 0x40000000
+   DO_TEST(0x70000000, L"1.75 GB");                   // 0x70000000
+   DO_TEST(0x80000000, L"2.00 GB");                   // 0x80000000
+   DO_TEST(0x100000000, L"4.00 GB");                  // 0x100000000
+   DO_TEST(1099511627776, L"1.00 TB");                // 0x10000000000
+   DO_TEST(1125899906842624, L"1.00 PB");             // 0x4000000000000
+   DO_TEST(1152921504606846976, L"1.00 EB");          // 0x1000000000000000
+   DO_TEST(2305843009213693952, L"2.00 EB");          // 0x2000000000000000
+   DO_TEST(4611686018427387904, L"4.00 EB");          // 0x4000000000000000
+   DO_TEST(0x7fffffffffffffff, L"7.99 EB");           // 0x7fffffffffffffff
+   DO_TEST(0x8000000000000000, L"0 bytes");           // 0x8000000000000000  High Bit Set Here
+   DO_TEST(0xffffffff00000000, L"0 bytes");           // 0xffffffff00000000
+   DO_TEST(0xffffffff00000001, L"1 bytes");           // 0xffffffff00000001
+   DO_TEST(0xffffffff70000000, L"1879048192 bytes");  // 0xffffffff70000000
+   DO_TEST(0xffffffff7fffffff, L"2147483647 bytes");  // 0xffffffff7fffffff
+   DO_TEST(0xffffffff80000000, L"-2147483648 bytes"); // 0xffffffff80000000 // Maximum Negative Number -2.00 GB
+   DO_TEST(0xffffffff80000001, L"-2147483647 bytes"); // 0xffffffff80000001
+   DO_TEST(0xffffffff90000000, L"-1879048192 bytes"); // 0xffffffff90000000
+   DO_TEST(-1073741824, L"-1073741824 bytes");        // 0xffffffffc0000000  -1.00 GB
+   DO_TEST(-1048576, L"-1048576 bytes");              // 0xfffffffffff00000  -1.00 MB
+   DO_TEST(-1024, L"-1024 bytes");                    // 0xfffffffffffffc00  -1.00 KB
+   DO_TEST(0xffffffffffffffff, L"-1 bytes");          // 0xffffffffffffffff
+
+   // Here are some large negative tests and they all return zero bytes
+
+   DO_TEST(-4294967296, L"0 bytes");           // 0xffffffff00000000
+   DO_TEST(-8589934592, L"0 bytes");           // 0xfffffffe00000000
+   DO_TEST(-17179869184, L"0 bytes");          // 0xfffffffc00000000
+   DO_TEST(-34359738368, L"0 bytes");          // 0xfffffff800000000
+   DO_TEST(-68719476736, L"0 bytes");          // 0xfffffff000000000
+   DO_TEST(-137438953472, L"0 bytes");         // 0xffffffe000000000
+   DO_TEST(-274877906944, L"0 bytes");         // 0xffffffc000000000
+   DO_TEST(-549755813888, L"0 bytes");         // 0xffffff8000000000
+   DO_TEST(-1099511627776, L"0 bytes");        // 0xffffff0000000000
+   DO_TEST(-1152921504606846976, L"0 bytes");  // 0xf000000000000000
+
+   // These statements create compile errors and seem to be compiler conversion related
+   //DO_TEST(2147483648, L"2.00 GB");         //  2.00 GB & This gives a compile error
+   //DO_TEST(-2147483648, L"0 bytes");        // -2.00 GB & This gives a compile error
+}
Index: rostests/apitests/shlwapi/testlist.c
===================================================================
--- rostests/apitests/shlwapi/testlist.c	(revision 73545)
+++ rostests/apitests/shlwapi/testlist.c	(working copy)
@@ -5,6 +5,7 @@
 extern void func_isuncpathserver(void);
 extern void func_isuncpathservershare(void);
 extern void func_PathUnExpandEnvStrings(void);
+extern void func_StrFormatByteSizeW(void);
 
 const struct test winetest_testlist[] =
 {
@@ -12,5 +13,6 @@
     { "PathIsUNCServer", func_isuncpathserver },
     { "PathIsUNCServerShare", func_isuncpathservershare },
     { "PathUnExpandEnvStrings", func_PathUnExpandEnvStrings },
+    { "StrFormatByteSizeW", func_StrFormatByteSizeW },
     { 0, 0 }
 };