Scripted test for fg built-in

Test script copied from:
https://github.com/magicant/yash/blob/5045f625ea142ec9b4fe60eb074ce8261a62d910/tests/fg-p.tst

yash/tests/scripted_test.rs

@@ -148,6 +148,11 @@ fn export_builtin() {
     run("export-p.sh")
 }
 
+#[test]
+fn fg_builtin() {
+    run_with_pty("fg-p.sh")
+}
+
 #[test]
 fn fnmatch() {
     run("fnmatch-p.sh")

yash/tests/scripted_test/fg-p.sh

@@ -0,0 +1,78 @@
+# fg-p.sh: test of the fg built-in for any POSIX-compliant shell
+
+posix="true"
+
+cat >job1 <<\__END__
+exec sh -c 'echo 1; kill -s STOP $$; echo 2'
+__END__
+
+cat >job2 <<\__END__
+exec sh -c 'echo a; kill -s STOP $$; echo b'
+__END__
+
+chmod a+x job1
+chmod a+x job2
+
+mkfifo fifo
+
+test_O -d -e n 'fg cannot be used when job control is disabled' +m
+:&
+fg
+__IN__
+
+test_oE 'default operand chooses most recently suspended job' -m
+:&
+sh -c 'kill -s STOP $$; echo 1'
+fg >/dev/null
+__IN__
+1
+__OUT__
+
+: TODO Needs to find a way to test this <<\__IN__
+test_oE 'resumed job is in foreground' -m
+sh -c 'kill -s STOP $$; ...'
+fg >/dev/null
+__IN__
+
+: TODO Needs the kill built-in <<\__IN__
+test_x -e 127 'resumed job is disowned unless suspended again' -m
+cat fifo >/dev/null &
+exec 3>fifo
+kill -s STOP %
+exec 3>&-
+fg >/dev/null
+wait $!
+__IN__
+
+test_oE 'specifying job ID' -m
+./job1
+./job2
+fg %./job1 >/dev/null
+fg %./job2 >/dev/null
+__IN__
+1
+a
+2
+b
+__OUT__
+
+test_oE 'fg prints resumed job' -m
+./job1
+fg
+__IN__
+1
+./job1
+2
+__OUT__
+
+test_O -d -e n 'no existing job' -m
+fg
+__IN__
+
+test_O -d -e n 'no such job' -m
+sh -c 'kill -s STOP $$'
+fg %_no_such_job_
+exit_status=$?
+fg >/dev/null
+exit $exit_status
+__IN__