diff --git a/lib/common/mock.c b/lib/common/mock.c
index 32ddd14dd5..93d41cbc22 100644
--- a/lib/common/mock.c
+++ b/lib/common/mock.c
@@ -1,330 +1,336 @@
 /*
  * Copyright 2021-2022 the Pacemaker project contributors
  *
  * The version control history for this file may have further details.
  *
  * This source code is licensed under the GNU Lesser General Public License
  * version 2.1 or later (LGPLv2.1+) WITHOUT ANY WARRANTY.
  */
 
 #include <errno.h>
 #include <pwd.h>
 #include <stdarg.h>
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <setjmp.h>
 #include <sys/types.h>
 #include <sys/utsname.h>
 #include <unistd.h>
 #include <grp.h>
 
 #include <cmocka.h>
 #include "mock_private.h"
 
 /* This file is only used when running "make check".  It is built into
  * libcrmcommon_test.a, not into libcrmcommon.so.  It is used to support
  * constructing mock versions of library functions for unit testing.
  *
  * HOW TO ADD A MOCKED FUNCTION:
  *
  * - In this file, declare a bool pcmk__mock_X variable, and define a __wrap_X
  *   function with the same prototype as the actual function that performs the
  *   desired behavior if pcmk__mock_X is true and calls __real_X otherwise.
  *   You can use cmocka's mock_type() and mock_ptr_type() to pass extra
  *   information to the mocked function (see existing examples for details).
  *
  * - In mock_private.h, add declarations for extern bool pcmk__mock_X and the
  *   __real_X and __wrap_X function prototypes.
  *
  * - In mk/tap.mk, add the function name to the WRAPPED variable.
  *
  * HOW TO USE A MOCKED FUNCTION:
  *
  * - #include "mock_private.h" in your test file.
  *
  * - Write your test cases using pcmk__mock_X and cmocka's will_return() as
  *   needed per the comments for the mocked function below. See existing test
  *   cases for examples.
  */
 
 // LCOV_EXCL_START
 /* calloc()
  *
  * If pcmk__mock_calloc is set to true, later calls to calloc() will return
  * NULL and must be preceded by:
  *
  *     expect_*(__wrap_calloc, nmemb[, ...]);
  *     expect_*(__wrap_calloc, size[, ...]);
  *
  * expect_* functions: https://api.cmocka.org/group__cmocka__param.html
  */
 
 bool pcmk__mock_calloc = false;
 
 void *
 __wrap_calloc(size_t nmemb, size_t size)
 {
     if (!pcmk__mock_calloc) {
         return __real_calloc(nmemb, size);
     }
     check_expected(nmemb);
     check_expected(size);
     return NULL;
 }
 
 
 /* getenv()
  *
  * If pcmk__mock_getenv is set to true, later calls to getenv() must be preceded
  * by:
  *
  *     expect_*(__wrap_getenv, name[, ...]);
  *     will_return(__wrap_getenv, return_value);
  *
  * expect_* functions: https://api.cmocka.org/group__cmocka__param.html
  */
 
 bool pcmk__mock_getenv = false;
 
 char *
 __wrap_getenv(const char *name)
 {
     if (!pcmk__mock_getenv) {
         return __real_getenv(name);
     }
     check_expected_ptr(name);
     return mock_ptr_type(char *);
 }
 
 
 /* getpid()
  *
  * If pcmk__mock_getpid is set to true, later calls to getpid() must be preceded
  * by:
  *
  *     will_return(__wrap_getpid, return_value);
  */
 
 bool pcmk__mock_getpid = false;
 
 pid_t
 __wrap_getpid(void)
 {
     return pcmk__mock_getpid? mock_type(pid_t) : __real_getpid();
 }
 
 
 /* setgrent(), getgrent() and endgrent()
  *
  * If pcmk__mock_grent is set to true, getgrent() will behave as if the only
  * groups on the system are:
  *
  * - grp0 (user0, user1)
  * - grp1 (user1)
  * - grp2 (user2, user1)
  */
 
 bool pcmk__mock_grent = false;
 
 // Index of group that will be returned next from getgrent()
 static int group_idx = 0;
 
 // Data used for testing
 static const char* grp0_members[] = {
     "user0", "user1", NULL
 };
 
 static const char* grp1_members[] = {
     "user1", NULL
 };
 
 static const char* grp2_members[] = {
     "user2", "user1", NULL
 };
 
 /* An array of "groups" (a struct from grp.h)
  *
  * The members of the groups are initalized here to some testing data, casting
  * away the consts to make the compiler happy and simplify initialization. We
  * never actually change these variables during the test!
  *
  * string literal = const char* (cannot be changed b/c ? )
  *                  vs. char* (it's getting casted to this)
  */
 static const int NUM_GROUPS = 3;
 static struct group groups[] = {
     {(char*)"grp0", (char*)"", 0, (char**)grp0_members},
     {(char*)"grp1", (char*)"", 1, (char**)grp1_members},
     {(char*)"grp2", (char*)"", 2, (char**)grp2_members},
 };
 
 // This function resets the group_idx to 0.
 void
 __wrap_setgrent(void) {
     if (pcmk__mock_grent) {
         group_idx = 0;
     } else {
         __real_setgrent();
     }
 }
 
 /* This function returns the next group entry in the list of groups, or
  * NULL if there aren't any left.
  * group_idx is a global variable which keeps track of where you are in the list
  */
 struct group *
 __wrap_getgrent(void) {
     if (pcmk__mock_grent) {
         if (group_idx >= NUM_GROUPS) {
             return NULL;
         }
         return &groups[group_idx++];
     } else {
         return __real_getgrent();
     }
 }
 
 void
 __wrap_endgrent(void) {
     if (!pcmk__mock_grent) {
         __real_endgrent();
     }
 }
 
 
 /* fopen()
  *
  * If pcmk__mock_fopen is set to true, later calls to fopen() must be
  * preceded by:
  *
+ *     expect_*(__wrap_fopen, pathname[, ...]);
+ *     expect_*(__wrap_fopen, mode[, ...]);
  *     will_return(__wrap_fopen, errno_to_set);
+ *
+ * expect_* functions: https://api.cmocka.org/group__cmocka__param.html
  */
 
 bool pcmk__mock_fopen = false;
 
 FILE *
 __wrap_fopen(const char *pathname, const char *mode)
 {
     if (pcmk__mock_fopen) {
+        check_expected_ptr(pathname);
+        check_expected_ptr(mode);
         errno = mock_type(int);
 
         if (errno != 0) {
             return NULL;
         } else {
             return __real_fopen(pathname, mode);
         }
 
     } else {
         return __real_fopen(pathname, mode);
     }
 }
 
 
 /* getpwnam_r()
  *
  * If pcmk__mock_getpwnam_r is set to true, later calls to getpwnam_r() must be
  * preceded by:
  *
  *     will_return(__wrap_getpwnam_r, return_value);
  *     will_return(__wrap_getpwnam_r, ptr_to_result_struct);
  */
 
 bool pcmk__mock_getpwnam_r = false;
 
 int
 __wrap_getpwnam_r(const char *name, struct passwd *pwd, char *buf,
                   size_t buflen, struct passwd **result)
 {
     if (pcmk__mock_getpwnam_r) {
         int retval = mock_type(int);
 
         *result = mock_ptr_type(struct passwd *);
         return retval;
 
     } else {
         return __real_getpwnam_r(name, pwd, buf, buflen, result);
     }
 }
 
 /*
  * If pcmk__mock_readlink is set to true, later calls to readlink() must be
  * preceded by:
  *
  *     will_return(__wrap_readlink, errno_to_set);
  *     will_return(__wrap_readlink, link_contents);
  *
  * The mocked function will return 0 if errno_to_set is 0, and -1 otherwise.
  */
 
 bool pcmk__mock_readlink = false;
 
 ssize_t
 __wrap_readlink(const char *restrict path, char *restrict buf,
                 size_t bufsize)
 {
     if (pcmk__mock_readlink) {
         const char *contents = NULL;
 
         errno = mock_type(int);
         contents = mock_ptr_type(const char *);
 
         if (errno == 0) {
             strncpy(buf, contents, bufsize - 1);
             return strlen(contents);
         }
         return -1;
 
     } else {
         return __real_readlink(path, buf, bufsize);
     }
 }
 
 
 /* strdup()
  *
  * If pcmk__mock_strdup is set to true, later calls to strdup() will return
  * NULL.
  */
 
 bool pcmk__mock_strdup = false;
 
 char *
 __wrap_strdup(const char *s)
 {
     return pcmk__mock_strdup? NULL : __real_strdup(s);
 }
 
 
 /* uname()
  *
  * If pcmk__mock_uname is set to true, later calls to uname() must be preceded
  * by:
  *
  *     will_return(__wrap_uname, return_value);
  *     will_return(__wrap_uname, node_name_for_buf_parameter_to_uname);
  */
 
 bool pcmk__mock_uname = false;
 
 int
 __wrap_uname(struct utsname *buf)
 {
     if (pcmk__mock_uname) {
         int retval = mock_type(int);
         char *result = mock_ptr_type(char *);
 
         if (result != NULL) {
             strcpy(buf->nodename, result);
         }
         return retval;
 
     } else {
         return __real_uname(buf);
     }
 }
 
 // LCOV_EXCL_STOP
diff --git a/lib/common/tests/output/pcmk__output_new_test.c b/lib/common/tests/output/pcmk__output_new_test.c
index 65f3b4d3ea..4d27436ff6 100644
--- a/lib/common/tests/output/pcmk__output_new_test.c
+++ b/lib/common/tests/output/pcmk__output_new_test.c
@@ -1,154 +1,156 @@
 /*
  * Copyright 2022 the Pacemaker project contributors
  *
  * The version control history for this file may have further details.
  *
  * This source code is licensed under the GNU Lesser General Public License
  * version 2.1 or later (LGPLv2.1+) WITHOUT ANY WARRANTY.
  */
 
 #include <crm_internal.h>
 
 #include <crm/common/unittest_internal.h>
 #include <crm/common/output_internal.h>
 
 #include "mock_private.h"
 
 static bool init_succeeds = true;
 
 static bool
 fake_text_init(pcmk__output_t *out) {
     return init_succeeds;
 }
 
 static void
 fake_text_free_priv(pcmk__output_t *out) {
     /* This function intentionally left blank */
 }
 
 /* "text" is the default for pcmk__output_new. */
 static pcmk__output_t *
 mk_fake_text_output(char **argv) {
     pcmk__output_t *retval = calloc(1, sizeof(pcmk__output_t));
 
     if (retval == NULL) {
         return NULL;
     }
 
     retval->fmt_name = "text";
     retval->init = fake_text_init;
     retval->free_priv = fake_text_free_priv;
 
     retval->register_message = pcmk__register_message;
     retval->message = pcmk__call_message;
 
     return retval;
 }
 
 static int
 setup(void **state) {
     pcmk__register_format(NULL, "text", mk_fake_text_output, NULL);
     return 0;
 }
 
 static int
 teardown(void **state) {
     pcmk__unregister_formats();
     return 0;
 }
 
 static void
 empty_formatters(void **state) {
     pcmk__output_t *out = NULL;
 
     pcmk__assert_asserts(pcmk__output_new(&out, "fake", NULL, NULL));
 }
 
 static void
 invalid_params(void **state) {
     /* This must be called with the setup/teardown functions so formatters is not NULL. */
     pcmk__assert_asserts(pcmk__output_new(NULL, "fake", NULL, NULL));
 }
 
 static void
 no_such_format(void **state) {
     pcmk__output_t *out = NULL;
 
     assert_int_equal(pcmk__output_new(&out, "fake", NULL, NULL), pcmk_rc_unknown_format);
 }
 
 static void
 create_fails(void **state) {
     pcmk__output_t *out = NULL;
 
     pcmk__mock_calloc = true;   // calloc() will return NULL
 
     expect_value(__wrap_calloc, nmemb, 1);
     expect_value(__wrap_calloc, size, sizeof(pcmk__output_t));
     assert_int_equal(pcmk__output_new(&out, "text", NULL, NULL), ENOMEM);
 
     pcmk__mock_calloc = false;  // Use real calloc()
 }
 
 static void
 fopen_fails(void **state) {
     pcmk__output_t *out = NULL;
 
     pcmk__mock_fopen = true;
+    expect_string(__wrap_fopen, pathname, "destfile");
+    expect_string(__wrap_fopen, mode, "w");
     will_return(__wrap_fopen, EPERM);
 
     assert_int_equal(pcmk__output_new(&out, "text", "destfile", NULL), EPERM);
 
     pcmk__mock_fopen = false;
 }
 
 static void
 init_fails(void **state) {
     pcmk__output_t *out = NULL;
 
     init_succeeds = false;
     assert_int_equal(pcmk__output_new(&out, "text", NULL, NULL), ENOMEM);
     init_succeeds = true;
 }
 
 static void
 everything_succeeds(void **state) {
     pcmk__output_t *out = NULL;
 
     assert_int_equal(pcmk__output_new(&out, "text", NULL, NULL), pcmk_rc_ok);
     assert_string_equal(out->fmt_name, "text");
     assert_ptr_equal(out->dest, stdout);
     assert_false(out->quiet);
     assert_non_null(out->messages);
     assert_string_equal(getenv("OCF_OUTPUT_FORMAT"), "text");
 
     pcmk__output_free(out);
 }
 
 static void
 no_fmt_name_given(void **state) {
     pcmk__output_t *out = NULL;
 
     assert_int_equal(pcmk__output_new(&out, NULL, NULL, NULL), pcmk_rc_ok);
     assert_string_equal(out->fmt_name, "text");
 
     pcmk__output_free(out);
 }
 
 int
 main(int argc, char **argv)
 {
     const struct CMUnitTest tests[] = {
         cmocka_unit_test(empty_formatters),
         cmocka_unit_test_setup_teardown(invalid_params, setup, teardown),
         cmocka_unit_test_setup_teardown(no_such_format, setup, teardown),
         cmocka_unit_test_setup_teardown(create_fails, setup, teardown),
         cmocka_unit_test_setup_teardown(init_fails, setup, teardown),
         cmocka_unit_test_setup_teardown(fopen_fails, setup, teardown),
         cmocka_unit_test_setup_teardown(everything_succeeds, setup, teardown),
         cmocka_unit_test_setup_teardown(no_fmt_name_given, setup, teardown),
     };
 
     cmocka_set_message_output(CM_OUTPUT_TAP);
     return cmocka_run_group_tests(tests, NULL, NULL);
 }