31665: zpty should attach terminal on slave.

Also add test.

Test/.distfiles

@@ -40,6 +40,7 @@ V04features.ztst
 V05styles.ztst
 V06parameter.ztst
 V07pcre.ztst
+V08zpty.ztst
 Y01completion.ztst
 Y02compmatch.ztst
 Y03arguments.ztst

Test/V08zpty.ztst

@@ -0,0 +1,20 @@
+# zpty is required by tests of interactive modes of the shell itself.
+# This tests some extra things.
+
+%prep
+
+  if ! zmodload zsh/zpty 2>/dev/null
+  then
+    ZTST_unimplemented="the zsh/zpty module is not available"
+    return 0
+  fi
+
+%test
+
+  zpty cat cat
+  print a line of text | zpty -w cat
+  var=
+  zpty -r cat var && print -r -- ${var%%$'\r\n'}
+  zpty -d cat
+0:zpty with a process that does not set up the terminal
+>a line of text