1 files changed, 49 insertions, 0 deletions
diff --git a/Lib/test/test_readline.py b/Lib/test/test_readline.py
index 35330ab076..84fd119e6a 100644
--- a/Lib/test/test_readline.py
+++ b/Lib/test/test_readline.py
@@ -1,7 +1,11 @@
 """
 Very minimal unittests for parts of the readline module.
 """
+from errno import EIO
 import os
+import selectors
+import subprocess
+import sys
 import tempfile
 import unittest
 from test.support import import_module, unlink
@@ -96,6 +100,51 @@ class TestReadline(unittest.TestCase):
                                               TERM='xterm-256color')
         self.assertEqual(stdout, b'')
 
+    auto_history_script = """\
+import readline
+readline.set_auto_history({})
+input()
+print("History length:", readline.get_current_history_length())
+"""
+
+    def test_auto_history_enabled(self):
+        output = run_pty(self.auto_history_script.format(True))
+        self.assertIn(b"History length: 1\r\n", output)
+
+    def test_auto_history_disabled(self):
+        output = run_pty(self.auto_history_script.format(False))
+        self.assertIn(b"History length: 0\r\n", output)
+
+
+def run_pty(script, input=b"dummy input\r"):
+    pty = import_module('pty')
+    output = bytearray()
+    [master, slave] = pty.openpty()
+    args = (sys.executable, '-c', script)
+    proc = subprocess.Popen(args, stdin=slave, stdout=slave, stderr=slave)
+    os.close(slave)
+    with proc, selectors.DefaultSelector() as sel:
+        sel.register(master, selectors.EVENT_READ | selectors.EVENT_WRITE)
+        os.set_blocking(master, False)
+        while True:
+            for [_, events] in sel.select():
+                if events & selectors.EVENT_READ:
+                    try:
+                        chunk = os.read(master, 0x10000)
+                    except OSError as err:
+                        # Linux raises EIO when the slave is closed
+                        if err.errno != EIO:
+                            raise
+                        chunk = b""
+                    if not chunk:
+                        os.close(master)
+                        return output
+                    output.extend(chunk)
+                if events & selectors.EVENT_WRITE:
+                    input = input[os.write(master, input):]
+                    if not input:
+                        sel.modify(master, selectors.EVENT_READ)
+
 
 if __name__ == "__main__":
     unittest.main()