test(conftest): prepare temporary file for HISTFILE

[Problem] We have previously set HISTFILE=/dev/null to leave user's
history file alone in the test, but it turned out to break the system.
When the number of history entries reach HISTFILESIZE, Bash tries to
replace the entity at $HISTFILE with a regular file.
HISTFILE=/dev/null causes the removal of the device /dev/null and
creation of a regular file at /dev/null.  This Bash behavior was fixed
in Bash 4.4 after the following bug-bash discussion:

https://lists.gnu.org/archive/html/bug-bash/2015-01/msg00138.html

[Solution] As a workaround, we prepare an empty temporary file for
each test.

[Remark] Another possible solution was to unset HISTFILE in
test/config/bashrc.  However test/config/bashrc is sourced after the
first prompt is shown, i.e., after the user's history file is loaded.
This doesn't necessarily cause problems, but we rather use an empty
file for the history to perform tests in a unqiue condition.

Author: akinomyoga

test/t/conftest.py

@@ -186,29 +186,55 @@ def partialize(
 def bash(request) -> pexpect.spawn:
 
     logfile = None
+    histfile = None
+    tmpdir = None
+    bash = None
+
     if os.environ.get("BASHCOMP_TEST_LOGFILE"):
         logfile = open(os.environ["BASHCOMP_TEST_LOGFILE"], "w")
     elif os.environ.get("CI"):
         logfile = sys.stdout
+
     testdir = os.path.abspath(
         os.path.join(os.path.dirname(__file__), os.pardir)
     )
-    env = os.environ.copy()
-    env.update(
-        dict(
-            SRCDIR=testdir,  # TODO needed at least by bashrc
-            SRCDIRABS=testdir,
-            PS1=PS1,
-            INPUTRC="%s/config/inputrc" % testdir,
-            TERM="dumb",
-            LC_COLLATE="C",  # to match Python's default locale unaware sort
-            HISTFILE="/dev/null",  # to leave user's history file alone
-        )
+
+    # Create an empty temporary file for HISTFILE.
+    #
+    # To prevent the tested Bash processes from writing to the user's
+    # history file or any other files, we prepare an empty temporary
+    # file for each test.
+    #
+    # - Note that HISTFILE=/dev/null may not work.  It results in the
+    #   removal of the device /dev/null and the creation of a regular
+    #   file at /dev/null when the number of commands reach
+    #   HISTFILESIZE by Bash-4.3's bug.  This causes the executation
+    #   of garbages through BASH_COMPLETION_USER_FILE=/dev/null.
+    # - Note also that "unset -v HISTFILE" in "test/config/bashrc" was
+    #   not adopted because "test/config/bashrc" is loaded after the
+    #   history is read from the history file.
+    #
+    histfile = tempfile.NamedTemporaryFile(
+        prefix="bash-completion-test_", delete=False
     )
 
-    tmpdir = None
-    bash = None
     try:
+        # release the file handle so that Bash can open the file.
+        histfile.close()
+
+        env = os.environ.copy()
+        env.update(
+            dict(
+                SRCDIR=testdir,  # TODO needed at least by bashrc
+                SRCDIRABS=testdir,
+                PS1=PS1,
+                INPUTRC="%s/config/inputrc" % testdir,
+                TERM="dumb",
+                LC_COLLATE="C",  # to match Python's default locale unaware sort
+                HISTFILE=histfile.name,
+            )
+        )
+
         marker = request.node.get_closest_marker("bashcomp")
 
         # Set up the current working directory
@@ -306,6 +332,11 @@ def bash(request) -> pexpect.spawn:
             bash.close()
         if tmpdir:
             tmpdir.cleanup()
+        if histfile:
+            try:
+                os.remove(histfile.name)
+            except OSError:
+                pass
         if logfile and logfile != sys.stdout:
             logfile.close()