Shell: Make tests use PASS/FAIL instead of exit codes

There's no guarantee that the last executed command will have a zero
exit code, and so the shell exit code may or may not be zero, even if
all the tests pass.
Also changes the `test || echo fail && exit` to
`if not test { echo fail && exit }`, since that's nicer-looking.

Userland/Shell/Tests/builtin-redir.sh

@@ -1,5 +1,7 @@
 #!/bin/sh
 
+source test-commons.inc
+
 rm -rf shell-test
 mkdir -p shell-test
 cd shell-test
@@ -7,11 +9,13 @@ cd shell-test
     time sleep 1 2>timeerr >timeout
     cat timeout
     # We cannot be sure about the values, so just assert that they're not empty.
-    test -n "$(cat timeerr)" || echo "Failure: 'time' stderr output not redirected correctly" && exit 1
-    test -e timeout || echo "Failure: 'time' stdout output not redirected correctly" && exit 1
+    if not test -n "$(cat timeerr)" { fail "'time' stderr output not redirected correctly" }
+    if not test -e timeout { fail "'time' stdout output not redirected correctly" }
 
     time ls 2> /dev/null | head > timeout
-    test -n "$(cat timeout)" || echo "Failure: 'time' stdout not piped correctly" && exit 1
+    if not test -n "$(cat timeout)" { fail "'time' stdout not piped correctly" }
 
 cd ..
 rm -rf shell-test # TODO: Remove this file at the end once we have `trap'
+
+echo PASS