[3.9] bpo-42789: Don't skip curses tests on non-tty. (GH-24009) (GH-24076)

If __stdout__ is not attached to terminal, try to use __stderr__
if it is attached to terminal, or open the terminal device, or
use regular file as terminal, but some functions will be untested
in the latter case.
(cherry picked from commit 607501abb4)

Lib/test/test_curses.py

@@ -47,37 +47,57 @@ class TestCurses(unittest.TestCase):
 
     @classmethod
     def setUpClass(cls):
-        if not sys.__stdout__.isatty():
-            # Temporary skip tests on non-tty
-            raise unittest.SkipTest('sys.__stdout__ is not a tty')
-            cls.tmp = tempfile.TemporaryFile()
-            fd = cls.tmp.fileno()
-        else:
-            cls.tmp = None
-            fd = sys.__stdout__.fileno()
         # testing setupterm() inside initscr/endwin
         # causes terminal breakage
-        curses.setupterm(fd=fd)
+        stdout_fd = sys.__stdout__.fileno()
-
+        curses.setupterm(fd=stdout_fd)
-    @classmethod
-    def tearDownClass(cls):
-        if cls.tmp:
-            cls.tmp.close()
-            del cls.tmp
 
     def setUp(self):
+        self.isatty = True
+        self.output = sys.__stdout__
+        stdout_fd = sys.__stdout__.fileno()
+        if not sys.__stdout__.isatty():
+            # initstr() unconditionally uses C stdout.
+            # If it is redirected to file or pipe, try to attach it
+            # to terminal.
+            # First, save a copy of the file descriptor of stdout, so it
+            # can be restored after finishing the test.
+            dup_fd = os.dup(stdout_fd)
+            self.addCleanup(os.close, dup_fd)
+            self.addCleanup(os.dup2, dup_fd, stdout_fd)
+
+            if sys.__stderr__.isatty():
+                # If stderr is connected to terminal, use it.
+                tmp = sys.__stderr__
+                self.output = sys.__stderr__
+            else:
+                try:
+                    # Try to open the terminal device.
+                    tmp = open('/dev/tty', 'wb', buffering=0)
+                except OSError:
+                    # As a fallback, use regular file to write control codes.
+                    # Some functions (like savetty) will not work, but at
+                    # least the garbage control sequences will not be mixed
+                    # with the testing report.
+                    tmp = tempfile.TemporaryFile(mode='wb', buffering=0)
+                    self.isatty = False
+                self.addCleanup(tmp.close)
+                self.output = None
+            os.dup2(tmp.fileno(), stdout_fd)
+
         self.save_signals = SaveSignals()
         self.save_signals.save()
-        if verbose:
+        self.addCleanup(self.save_signals.restore)
+        if verbose and self.output is not None:
             # just to make the test output a little more readable
-            print()
+            sys.stderr.flush()
+            sys.stdout.flush()
+            print(file=self.output, flush=True)
         self.stdscr = curses.initscr()
+        if self.isatty:
             curses.savetty()
-
+            self.addCleanup(curses.endwin)
-    def tearDown(self):
+            self.addCleanup(curses.resetty)
-        curses.resetty()
-        curses.endwin()
-        self.save_signals.restore()
 
     def test_window_funcs(self):
         "Test the methods of windows"
@@ -95,7 +115,7 @@ class TestCurses(unittest.TestCase):
         for meth in [stdscr.clear, stdscr.clrtobot,
                      stdscr.clrtoeol, stdscr.cursyncup, stdscr.delch,
                      stdscr.deleteln, stdscr.erase, stdscr.getbegyx,
-                     stdscr.getbkgd, stdscr.getkey, stdscr.getmaxyx,
+                     stdscr.getbkgd, stdscr.getmaxyx,
                      stdscr.getparyx, stdscr.getyx, stdscr.inch,
                      stdscr.insertln, stdscr.instr, stdscr.is_wintouched,
                      win.noutrefresh, stdscr.redrawwin, stdscr.refresh,
@@ -206,6 +226,11 @@ class TestCurses(unittest.TestCase):
         if hasattr(stdscr, 'enclose'):
             stdscr.enclose(10, 10)
 
+        with tempfile.TemporaryFile() as f:
+            self.stdscr.putwin(f)
+            f.seek(0)
+            curses.getwin(f)
+
         self.assertRaises(ValueError, stdscr.getstr, -400)
         self.assertRaises(ValueError, stdscr.getstr, 2, 3, -400)
         self.assertRaises(ValueError, stdscr.instr, -2)
@@ -224,14 +249,17 @@ class TestCurses(unittest.TestCase):
     def test_module_funcs(self):
         "Test module-level functions"
         for func in [curses.baudrate, curses.beep, curses.can_change_color,
-                     curses.cbreak, curses.def_prog_mode, curses.doupdate,
+                     curses.doupdate, curses.flash, curses.flushinp,
-                     curses.flash, curses.flushinp,
                      curses.has_colors, curses.has_ic, curses.has_il,
                      curses.isendwin, curses.killchar, curses.longname,
-                     curses.nocbreak, curses.noecho, curses.nonl,
+                     curses.noecho, curses.nonl, curses.noqiflush,
-                     curses.noqiflush, curses.noraw,
+                     curses.termattrs, curses.termname, curses.erasechar]:
-                     curses.reset_prog_mode, curses.termattrs,
+            with self.subTest(func=func.__qualname__):
-                     curses.termname, curses.erasechar]:
+                func()
+        if self.isatty:
+            for func in [curses.cbreak, curses.def_prog_mode,
+                         curses.nocbreak, curses.noraw,
+                         curses.reset_prog_mode]:
                 with self.subTest(func=func.__qualname__):
                     func()
         if hasattr(curses, 'filter'):
@@ -245,12 +273,8 @@ class TestCurses(unittest.TestCase):
         curses.delay_output(1)
         curses.echo() ; curses.echo(1)
 
-        with tempfile.TemporaryFile() as f:
-            self.stdscr.putwin(f)
-            f.seek(0)
-            curses.getwin(f)
-
         curses.halfdelay(1)
+        if self.isatty:
             curses.intrflush(1)
         curses.meta(1)
         curses.napms(100)
@@ -260,6 +284,7 @@ class TestCurses(unittest.TestCase):
         curses.nl() ; curses.nl(1)
         curses.putp(b'abc')
         curses.qiflush()
+        if self.isatty:
             curses.raw() ; curses.raw(1)
         curses.set_escdelay(25)
         self.assertEqual(curses.get_escdelay(), 25)
@@ -286,7 +311,7 @@ class TestCurses(unittest.TestCase):
         curses.init_pair(2, 1,1)
         curses.color_content(1)
         curses.color_pair(2)
-        curses.pair_content(curses.COLOR_PAIRS - 1)
+        curses.pair_content(min(curses.COLOR_PAIRS - 1, 0x7fff))
         curses.pair_number(0)
 
         if hasattr(curses, 'use_default_colors'):
@@ -358,7 +383,6 @@ class TestCurses(unittest.TestCase):
 
     @requires_curses_func('resizeterm')
     def test_resizeterm(self):
-        stdscr = self.stdscr
         lines, cols = curses.LINES, curses.COLS
         new_lines = lines - 1
         new_cols = cols + 1