test stdout stderr for TAP

tests/TAP/.expected-output

@@ -1,6 +1,8 @@
 # Begin - .testsuite/
 not ok 1 - a
 # ------------ Begin output ------------
+# This is stderr from a.
+# This is stdout from a.
 # ------------ End output ------------
 ok 2 - b
 ok 3 - # SKIP c

tests/TAP/.testsuite/a

@@ -1 +1,4 @@
+#!/bin/sh
+echo This is stderr from a. > /dev/stderr
+echo This is stdout from a. > /dev/stdout
 false

tests/TAP/.testsuite/b

@@ -1 +1,4 @@
+#!/bin/sh
+echo This is stderr from b. > /dev/stderr
+echo This is stdout from b. > /dev/stdout
 true