Document that 'make-process' mixes the output streams

* doc/lispref/processes.texi (Asynchronous Processes):
* src/process.c (Fmake_process): Document that standard error is mixed
with standard output if STDERR is nil.

* test/src/process-tests.el (make-process/mix-stderr): New unit test.

1 files changed, 18 insertions, 0 deletions

diff --git a/test/src/process-tests.el b/test/src/process-tests.el
index 7d355602297..849676ea8f0 100644
--- a/test/src/process-tests.el
+++ b/test/src/process-tests.el
@@ -181,5 +181,23 @@
               (should-not (process-query-on-exit-flag process))))
         (kill-process process)))))
 
+(ert-deftest make-process/mix-stderr ()
+  "Check that ‘make-process’ mixes the output streams if STDERR is nil."
+  (skip-unless (executable-find shell-file-name))
+  (with-temp-buffer
+    (let ((process (make-process
+                    :name "mix-stderr"
+                    :command (list shell-file-name shell-command-switch
+                                   "echo stdout && echo stderr >&2")
+                    :buffer (current-buffer)
+                    :sentinel #'ignore
+                    :noquery t
+                    :connection-type 'pipe)))
+      (while (process-live-p process)
+        (accept-process-output process))
+      (should (eq (process-status process) 'exit))
+      (should (eq (process-exit-status process) 0))
+      (should (equal (buffer-string) "stdout\nstderr\n")))))
+
 (provide 'process-tests)
 ;; process-tests.el ends here.