[1/3] msvcrt/tests: Add a test for fwrite flushing behavior.

[Grazvydas Ignotas]

---
IDA (latest paid version) breaks without early 4K write flushing.

 dlls/msvcrt/tests/file.c |   35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/dlls/msvcrt/tests/file.c b/dlls/msvcrt/tests/file.c
index f6a1624..37e6816 100644
--- a/dlls/msvcrt/tests/file.c
+++ b/dlls/msvcrt/tests/file.c
@@ -2219,6 +2219,40 @@ static void test__open_osfhandle(void)
     CloseHandle(tmp);
 }
 
+static void test_write_flush(void)
+{
+    static const char outbuffer[BUFSIZ * 16] = "0,1,2,3,4,5,6,7,8,9";
+    char inbuffer[BUFSIZ];
+    char *tempf;
+    FILE *file;
+    size_t size;
+    int fd;
+
+    tempf = _tempnam(".","wne");
+    file = fopen(tempf, "wb+");
+    ok(file != NULL, "unable to create test file\n");
+    fd = fileno(file);
+    for (size = BUFSIZ; size <= sizeof(outbuffer); size += BUFSIZ)
+    {
+        rewind(file);
+        ok(fwrite(outbuffer, 1, size, file) == size, "write failed\n");
+        /* lseek() below intentionally redirects the write in fflush() to detect
+         * if fwrite() has already flushed the whole buffer or not.
+         */
+        lseek(fd, 1, SEEK_SET);
+        fflush(file);
+        fseek(file, 0, SEEK_SET);
+        ok(fread(inbuffer, 1, sizeof(inbuffer), file) == sizeof(inbuffer), "read failed\n");
+        if (size % 4096 == 0)
+          todo_wine ok(memcmp(outbuffer, inbuffer, sizeof(inbuffer)) == 0, "missing flush by %d byte write\n", size);
+        else
+          ok(memcmp(outbuffer, inbuffer, sizeof(inbuffer)) != 0, "unexpected flush by %d byte write\n", size);
+    }
+    fclose(file);
+    unlink(tempf);
+    free(tempf);
+}
+
 START_TEST(file)
 {
     int arg_c;
@@ -2284,6 +2318,7 @@ START_TEST(file)
     test_stdin();
     test_mktemp();
     test__open_osfhandle();
+    test_write_flush();
 
     /* Wait for the (_P_NOWAIT) spawned processes to finish to make sure the report
      * file contains lines in the correct order
-- 
1.7.9.5