Disable test for non-standard platforms

- the specific test may fail under non-Linux
  *nix systems due to different pipe implementations
- fixes #768

Author: mrbean-bremen

pyfakefs/tests/fake_os_test.py

@@ -2812,6 +2812,10 @@ def test_write_to_pipe(self):
         self.os.close(read_fd)
         self.os.close(write_fd)
 
+    @unittest.skipIf(
+        sys.platform not in ("win32", "darwin", "linux"),
+        "Pipe implementation may differ on other platforms",
+    )
     def test_write_to_read_fd(self):
         read_fd, write_fd = self.os.pipe()
         self.assert_raises_os_error(errno.EBADF, self.os.write, read_fd, b"test")