On some systems (like Solaris), the master end of a tty/pty pair is

Yhg1s · Yhg1s · commit f2c1be22f2f6 · 2000-10-03T16:51:08.000Z
apparently not considered a terminal, and so isatty(3) returns false. So we
skip the test for ttyness of the master side and just check the slave side,
which should really be a terminal.
diff --git a/Lib/test/test_pty.py b/Lib/test/test_pty.py
@@ -27,8 +27,6 @@ def debug(msg):
     # " An optional feature could not be imported " ... ?
     raise TestSkipped, "Pseudo-terminals (seemingly) not functional."
 
-if not os.isatty(master_fd):
-    raise TestFailed, "master_fd is not a tty"
 if not os.isatty(slave_fd):
     raise TestFailed, "slave_fd is not a tty"
 
