; Adjust Eshell regression tests to avoid SIGPIPE

In batch mode, SIGPIPEs can cause Emacs to abort (bug#66186).

* lisp/eshell/esh-io.el (eshell-output-object-to-target): Update
comment.

* test/lisp/eshell/esh-proc-tests.el
(esh-proc-test/pipeline-connection-type/middle)
(esh-proc-test/pipeline-connection-type/last): Use '(ignore)', since
that causes no output when called with no arguments, thus avoiding a
risky 'process-send-string'.

lisp/eshell/esh-io.el

@@ -648,8 +648,11 @@ Returns what was actually sent, or nil if nothing was sent.")
       (process-send-string target object)
     (error
      ;; If `process-send-string' raises an error and the process has
-     ;; finished, treat it as a broken pipe.  Otherwise, just
-     ;; re-throw the signal.
+     ;; finished, treat it as a broken pipe.  Otherwise, just re-raise
+     ;; the signal.  NOTE: When running Emacs in batch mode
+     ;; (e.g. during regression tests), Emacs can abort due to SIGPIPE
+     ;; here.  Maybe `process-send-string' should handle SIGPIPE even
+     ;; in batch mode (bug#66186).
      (if (process-live-p target)
          (signal (car err) (cdr err))
        (signal 'eshell-pipe-broken (list target)))))

test/lisp/eshell/esh-proc-tests.el

@@ -174,23 +174,17 @@
 pipeline."
   (skip-unless (and (executable-find "sh")
                     (executable-find "cat")))
-  ;; An `eshell-pipe-broken' signal might occur internally; let Eshell
-  ;; handle it!
-  (let ((debug-on-error nil))
-    (eshell-command-result-equal
-     (concat "echo hi | " esh-proc-test--detect-pty-cmd " | cat")
-     nil)))
+  (eshell-command-result-equal
+   (concat "(ignore) | " esh-proc-test--detect-pty-cmd " | cat")
+   nil))
 
 (ert-deftest esh-proc-test/pipeline-connection-type/last ()
   "Test that only output streams are PTYs when a command ends a pipeline."
   (skip-unless (executable-find "sh"))
-  ;; An `eshell-pipe-broken' signal might occur internally; let Eshell
-  ;; handle it!
-  (let ((debug-on-error nil))
-    (eshell-command-result-equal
-     (concat "echo hi | " esh-proc-test--detect-pty-cmd)
-     (unless (eq system-type 'windows-nt)
-       "stdout\nstderr\n"))))
+  (eshell-command-result-equal
+   (concat "(ignore) | " esh-proc-test--detect-pty-cmd)
+   (unless (eq system-type 'windows-nt)
+     "stdout\nstderr\n")))
 
 
 ;; Synchronous processes