Add pipeline tests

This adds a pipeline test covering the fix in the prior commit,
related to #5675. Note #5675 is NOT fully fixed by this.

tests/interactive.expect.rc

@@ -5,6 +5,7 @@ log_file -noappend interactive.tmp.log
 
 set fish ../test/root/bin/fish
 set fish_key_reader ../test/root/bin/fish_key_reader
+set fish_test_helper ../test/root/bin/fish_test_helper
 
 set timeout 5
 

tests/pipeline.expect

@@ -0,0 +1,16 @@
+# vim: set filetype=expect:
+spawn $fish
+expect_prompt
+
+send_line "function echo_wrap ; /bin/echo $argv ; sleep 0.1;  ; end"
+expect_prompt
+
+set timeout 10
+for {set x 0} {$x<15} {incr x} {
+  send_line "echo_wrap 1 2 3 4 | $fish_test_helper become_foreground_then_print_stderr ; or exit 1"
+  expect_prompt "become_foreground_then_print_stderr done" {} unmatched { puts stderr "fish_test_helper become_foreground_then_print_stderr failed"}
+}
+
+# 'not' because we expect to have no jobs, in which case `jobs` will return false
+send_line "not jobs"
+expect_prompt "jobs: There are no jobs" {} unmatched { puts stderr "Should be no jobs" }