testConstraint testobj		[llength [info commands testobj]]
testConstraint testservicemode  [llength [info commands testservicemode]]
# Some things fail under Windows in Continuous Integration systems for subtle
# reasons such as CI often running with elevated privileges in a container.
testConstraint notWinCI [expr {
    $::tcl_platform(platform) ne "windows" || ![info exists ::env(CI)]}]
testConstraint notOSX [expr {$::tcl_platform(os) ne "Darwin"}]
# File permissions broken on wsl without some "exotic" wsl configuration
testConstraint notWsl [expr {[llength [array names ::env *WSL*]] == 0}]

# You need a *very* special environment to do some tests.  In
# particular, many file systems do not support large-files...
testConstraint largefileSupport [expr {$::tcl_platform(os) ne "Darwin"}]

# some tests can only be run is umask is 2
# if "umask" cannot be run, the tests will be skipped.

    set x [gets $f]
    close $f
    set f [open $path(test3) r]
    lappend x [gets $f]
    close $f
    set x
} {zzy abzzy}
test io-40.2 {POSIX open access modes: CREAT} {unix notWsl} {
    file delete $path(test3)
    set f [open $path(test3) {WRONLY CREAT} 0o600]
    file stat $path(test3) stats
    set x [format "0o%o" [expr {$stats(mode)&0o777}]]
    puts $f "line 1"
    close $f
    set f [open $path(test3) r]
    lappend x [gets $f]
    close $f
    set x
} {0o600 {line 1}}
test io-40.3 {POSIX open access modes: CREAT} {unix umask notWsl} {
    # This test only works if your umask is 2, like ouster's.
    file delete $path(test3)
    set f [open $path(test3) {WRONLY CREAT}]
    close $f
    file stat $path(test3) stats
    format 0o%03o [expr {$stats(mode)&0o777}]
} [format 0o%03o [expr {0o666 & ~ $umaskValue}]]

		fcopy $b $a -command [list geof $b]
		puts stderr 2COPY
	    }
	    puts stderr ...
	}
	puts stderr SRV
	set l {}
	set srv [socket -server new -myaddr 127.0.0.1 0]
        set port [lindex [fconfigure $srv -sockname] 2]
	puts stderr WAITING
	fileevent stdin readable bye
	puts "OK $port"
	vwait forever
    }
    # wait for OK from server.
    lassign [gets $pipe] ok port
    # Now the two clients.
    proc ::done {sock} {
	if {[eof $sock]} { close $sock ; return }
	lappend ::forever [gets $sock]
	return
    }
    set a [socket 127.0.0.1 $port]
    set b [socket 127.0.0.1 $port]
    fconfigure $a -translation binary -buffering none
    fconfigure $b -translation binary -buffering none
    fileevent  $a readable [list ::done $a]
    fileevent  $b readable [list ::done $b]
} -constraints {stdio fcopy} -body {
    # Now pass data through the server in both directions.
    set ::forever {}