diff --git a/.github/workflows/macos_tests.yaml b/.github/workflows/macos_tests.yaml
index 1c3547d96..4dde326aa 100644
--- a/.github/workflows/macos_tests.yaml
+++ b/.github/workflows/macos_tests.yaml
@@ -13,6 +13,8 @@ jobs:
     env:
       CONFIGURE_OPTS: --prefix=/tmp/modules --with-loadedmodules=null:dot --with-tcl=/opt/homebrew/lib --with-tclsh=/opt/homebrew/bin/tclsh
       COVERAGE: y
+      EXTRA_SCRIPT_PRETEST: make install-testsiteconfig-1 && export TESTSUITE_ENABLE_SITECONFIG=1
+      EXTRA_SCRIPT_POSTTEST: unset TESTSUITE_ENABLE_SITECONFIG
     steps:
       - uses: actions/checkout@v6
         with:
@@ -30,8 +32,15 @@ jobs:
           make
       - name: Test Modules build
         run: |
+          # specific compiling to enable DYLD library insertion
+          for f in lib/testutil-*.c; do
+            n=$(basename "$f" .c)
+            clang -dynamiclib -arch arm64 -arch arm64e -o lib/lib${n}.dylib lib/${n}.c
+          done
+          eval $EXTRA_SCRIPT_PRETEST
           make test-deps
           script/mt
+          eval $EXTRA_SCRIPT_POSTTEST
       - name: Install Modules
         run: |
           make install
diff --git a/.hunspell.en.dic b/.hunspell.en.dic
index 0c40f8703..a6f852e95 100644
--- a/.hunspell.en.dic
+++ b/.hunspell.en.dic
@@ -1334,3 +1334,5 @@ YYYYMMDD
 roadmap
 CI
 GHA
+ts
+OSX
diff --git a/lib/testutil-0getgroups.c b/lib/testutil-0getgroups.c
index 8786a1be6..e4fdc0656 100644
--- a/lib/testutil-0getgroups.c
+++ b/lib/testutil-0getgroups.c
@@ -1,7 +1,7 @@
 /*************************************************************************
  *
  * TESTUTIL-GETGROUPS.C, Superseded getgroups function for test purpose
- * Copyright (C) 2020-2021 Xavier Delaruelle
+ * Copyright (C) 2020-2026 Xavier Delaruelle
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -22,7 +22,7 @@
 
 int getgroups(int size, gid_t list[])
 {
-    return 0;
+   return 0;
 }
 
 /* vim:set tabstop=3 shiftwidth=3 expandtab autoindent: */
diff --git a/lib/testutil-closedir.c b/lib/testutil-closedir.c
index 0a6e3374a..f985b3212 100644
--- a/lib/testutil-closedir.c
+++ b/lib/testutil-closedir.c
@@ -1,7 +1,7 @@
 /*************************************************************************
  *
  * TESTUTIL-CLOSEDIR.C, Superseded closedir function for test purpose
- * Copyright (C) 2019-2021 Xavier Delaruelle
+ * Copyright (C) 2019-2026 Xavier Delaruelle
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,9 +20,30 @@
 
 #include <dirent.h>
 
+#if defined (__APPLE__)
+
+int my_closedir(DIR *dirp)
+{
+   return -1;
+}
+
+/* Code injection with DYLD interposing */
+__attribute__((used))
+static struct {
+   const void *replacement;
+   const void *replacee;
+} interposers[]
+__attribute__((section("__DATA,__interpose"))) = {
+   { (const void *)my_closedir, (const void *)closedir }
+};
+
+#else
+
 int closedir(DIR *dirp)
 {
-    return -1;
+   return -1;
 }
 
+#endif
+
 /* vim:set tabstop=3 shiftwidth=3 expandtab autoindent: */
diff --git a/lib/testutil-getgroups.c b/lib/testutil-getgroups.c
index ee5acadbb..2b388dcbc 100644
--- a/lib/testutil-getgroups.c
+++ b/lib/testutil-getgroups.c
@@ -1,7 +1,7 @@
 /*************************************************************************
  *
  * TESTUTIL-GETGROUPS.C, Superseded getgroups function for test purpose
- * Copyright (C) 2020-2021 Xavier Delaruelle
+ * Copyright (C) 2020-2026 Xavier Delaruelle
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -22,7 +22,7 @@
 
 int getgroups(int size, gid_t list[])
 {
-    return -1;
+   return -1;
 }
 
 /* vim:set tabstop=3 shiftwidth=3 expandtab autoindent: */
diff --git a/lib/testutil-getpwuid.c b/lib/testutil-getpwuid.c
index 9a7522f7b..ceaa7125b 100644
--- a/lib/testutil-getpwuid.c
+++ b/lib/testutil-getpwuid.c
@@ -1,7 +1,7 @@
 /*************************************************************************
  *
  * TESTUTIL-GETPWUID.C, Superseded getpwuid function for test purpose
- * Copyright (C) 2020-2021 Xavier Delaruelle
+ * Copyright (C) 2020-2026 Xavier Delaruelle
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -21,9 +21,30 @@
 #include <stddef.h>
 #include <pwd.h>
 
+#if defined (__APPLE__)
+
+struct passwd *my_getpwuid(uid_t uid)
+{
+   return NULL;
+}
+
+/* Code injection with DYLD interposing */
+__attribute__((used))
+static struct {
+   const void *replacement;
+   const void *replacee;
+} interposers[]
+__attribute__((section("__DATA,__interpose"))) = {
+   { (const void *)my_getpwuid, (const void *)getpwuid }
+};
+
+#else
+
 struct passwd *getpwuid(uid_t uid)
 {
-    return NULL;
+   return NULL;
 }
 
+#endif
+
 /* vim:set tabstop=3 shiftwidth=3 expandtab autoindent: */
diff --git a/lib/testutil-mktime.c b/lib/testutil-mktime.c
index 2cc83605e..08d07e3b4 100644
--- a/lib/testutil-mktime.c
+++ b/lib/testutil-mktime.c
@@ -1,7 +1,7 @@
 /*************************************************************************
  *
  * TESTUTIL-MKTIME.C, Superseded mktime function for test purpose
- * Copyright (C) 2020-2021 Xavier Delaruelle
+ * Copyright (C) 2020-2026 Xavier Delaruelle
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,9 +20,30 @@
 
 #include <time.h>
 
+#if defined (__APPLE__)
+
+time_t my_mktime(struct tm *tm)
+{
+   return -1;
+}
+
+/* Code injection with DYLD interposing */
+__attribute__((used))
+static struct {
+   const void *replacement;
+   const void *replacee;
+} interposers[]
+__attribute__((section("__DATA,__interpose"))) = {
+   { (const void *)my_mktime, (const void *)mktime }
+};
+
+#else
+
 time_t mktime(struct tm *tm)
 {
-    return -1;
+   return -1;
 }
 
+#endif
+
 /* vim:set tabstop=3 shiftwidth=3 expandtab autoindent: */
diff --git a/lib/testutil-time.c b/lib/testutil-time.c
index f76d04f1a..fe8d231b8 100644
--- a/lib/testutil-time.c
+++ b/lib/testutil-time.c
@@ -1,7 +1,7 @@
 /*************************************************************************
  *
  * TESTUTIL-TIME.C, Superseded time function for test purpose
- * Copyright (C) 2020-2021 Xavier Delaruelle
+ * Copyright (C) 2020-2026 Xavier Delaruelle
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,9 +20,30 @@
 
 #include <time.h>
 
+#if defined (__APPLE__)
+
+time_t my_time(time_t *tloc)
+{
+   return -1;
+}
+
+/* Code injection with DYLD interposing */
+__attribute__((used))
+static struct {
+   const void *replacement;
+   const void *replacee;
+} interposers[]
+__attribute__((section("__DATA,__interpose"))) = {
+   { (const void *)my_time, (const void *)time }
+};
+
+#else
+
 time_t time(time_t *tloc)
 {
-    return -1;
+   return -1;
 }
 
+#endif
+
 /* vim:set tabstop=3 shiftwidth=3 expandtab autoindent: */
diff --git a/testsuite/example/siteconfig.tcl-1 b/testsuite/example/siteconfig.tcl-1
index 32a89c582..87dee3b03 100644
--- a/testsuite/example/siteconfig.tcl-1
+++ b/testsuite/example/siteconfig.tcl-1
@@ -145,6 +145,11 @@ if {[info exists env(TESTSUITE_ENABLE_SITECONFIG_TCLEXTLIBFAILEDGETPWUID)]} {
     if {[catch {initStateUsername} errMsg]} {
         reportError $errMsg
     }
+    if {$tcl_platform(os) eq "Darwin"} {
+        if {[catch {[initStateUsergroups]} errMsg]} {
+            reportError $errMsg
+        }
+    }
 }
 
 # test tcl ext lib procedures against a failed getgroups call
diff --git a/testsuite/modules.00-init/120-siteconfig.exp b/testsuite/modules.00-init/120-siteconfig.exp
index 387c5a75a..258bd3c3e 100644
--- a/testsuite/modules.00-init/120-siteconfig.exp
+++ b/testsuite/modules.00-init/120-siteconfig.exp
@@ -410,14 +410,22 @@ if {[info exists tclextlib_file]} {
 # test tcl ext lib procedures against a failed closedir call
 if {[info exists closedirlib_file] && [file exists $closedirlib_file]} {
     setenv_var TESTSUITE_ENABLE_SITECONFIG_TCLEXTLIBFAILEDCLOSEDIR 1
-    setenv_var LD_PRELOAD $closedirlib_file
+    if {$tcl_platform(os) ne "Darwin"} {
+        setenv_var LD_PRELOAD $closedirlib_file
+    } else {
+        setenv_var DYLD_INSERT_LIBRARIES $closedirlib_file
+    }
     set ans [list]
-    lappend ans "$error_msgs: couldn't close directory \"$modpathre\": Success"
+    lappend ans "$error_msgs: couldn't close directory \"$modpathre\": .*"
     lappend ans $vers_reportre
     testouterr_cmd_re sh -V OK [join $ans \n]
 
     unsetenv_var TESTSUITE_ENABLE_SITECONFIG_TCLEXTLIBFAILEDCLOSEDIR
-    unsetenv_var LD_PRELOAD
+    if {$tcl_platform(os) ne "Darwin"} {
+        unsetenv_var LD_PRELOAD
+    } else {
+        unsetenv_var DYLD_INSERT_LIBRARIES
+    }
 } elseif {$verbose} {
     send_user "\tSkip tcl ext lib erroneous procedure calls as closedir test lib is not available\n"
 }
@@ -425,18 +433,31 @@ if {[info exists closedirlib_file] && [file exists $closedirlib_file]} {
 # test tcl ext lib procedures against a failed getpwuid call
 if {[info exists getpwuidlib_file] && [file exists $getpwuidlib_file]} {
     setenv_var TESTSUITE_ENABLE_SITECONFIG_TCLEXTLIBFAILEDGETPWUID 1
-    setenv_var LD_PRELOAD $getpwuidlib_file
+    if {$tcl_platform(os) ne "Darwin"} {
+        setenv_var LD_PRELOAD $getpwuidlib_file
+    } else {
+        setenv_var DYLD_INSERT_LIBRARIES $getpwuidlib_file
+    }
     set ans [list]
     lappend ans "$error_msgs: couldn't find name for user id \"$userid\": .*"
+    if {$tcl_platform(os) eq "Darwin"} {
+        lappend ans "$error_msgs: couldn't find name for user id \"$userid\": .*"
+    }
     lappend ans $vers_reportre
     testouterr_cmd_re sh -V OK [join $ans \n]
 
     unsetenv_var TESTSUITE_ENABLE_SITECONFIG_TCLEXTLIBFAILEDGETPWUID
-    unsetenv_var LD_PRELOAD
+    if {$tcl_platform(os) ne "Darwin"} {
+        unsetenv_var LD_PRELOAD
+    } else {
+        unsetenv_var DYLD_INSERT_LIBRARIES
+    }
 } elseif {$verbose} {
     send_user "\tSkip tcl ext lib erroneous procedure calls as getpwuid test lib is not available\n"
 }
 
+# getgroups syscall is not used on Darwin
+if {$tcl_platform(os) ne "Darwin"} {
 # test tcl ext lib procedures against a failed getgroups call
 if {[info exists getgroupslib_file] && [file exists $getgroupslib_file]} {
     setenv_var TESTSUITE_ENABLE_SITECONFIG_TCLEXTLIBFAILEDGETGROUPS 1
@@ -481,18 +502,27 @@ if {[info exists dupgetgroupslib_file] && [file exists $dupgetgroupslib_file]} {
 } elseif {$verbose} {
     send_user "\tSkip tcl ext lib erroneous procedure calls as dupgetgroups test lib is not available\n"
 }
+}
 
 # test tcl ext lib procedures against a failed time call
 if {[info exists timelib_file] && [file exists $timelib_file]} {
     setenv_var TESTSUITE_ENABLE_SITECONFIG_TCLEXTLIBFAILEDTIME 1
-    setenv_var LD_PRELOAD $timelib_file
+    if {$tcl_platform(os) ne "Darwin"} {
+        setenv_var LD_PRELOAD $timelib_file
+    } else {
+        setenv_var DYLD_INSERT_LIBRARIES $timelib_file
+    }
     set ans [list]
     lappend ans "$error_msgs: couldn't get Epoch time: .*"
     lappend ans $vers_reportre
     testouterr_cmd_re sh -V OK [join $ans \n]
 
     unsetenv_var TESTSUITE_ENABLE_SITECONFIG_TCLEXTLIBFAILEDTIME
-    unsetenv_var LD_PRELOAD
+    if {$tcl_platform(os) ne "Darwin"} {
+        unsetenv_var LD_PRELOAD
+    } else {
+        unsetenv_var DYLD_INSERT_LIBRARIES
+    }
 } elseif {$verbose} {
     send_user "\tSkip tcl ext lib erroneous procedure calls as time test lib is not available\n"
 }
@@ -508,14 +538,22 @@ unsetenv_var TESTSUITE_ENABLE_SITECONFIG_PARSEDATETIMEARG_NOARG
 # test tcl ext lib procedures against a failed mktime call
 if {[info exists mktimelib_file] && [file exists $mktimelib_file]} {
     setenv_var TESTSUITE_ENABLE_SITECONFIG_TCLEXTLIBFAILEDMKTIME 1
-    setenv_var LD_PRELOAD $mktimelib_file
+    if {$tcl_platform(os) ne "Darwin"} {
+        setenv_var LD_PRELOAD $mktimelib_file
+    } else {
+        setenv_var DYLD_INSERT_LIBRARIES $mktimelib_file
+    }
     set ans [list]
     lappend ans "$error_msgs: couldn't convert to Epoch time: .*"
     lappend ans $vers_reportre
     testouterr_cmd_re sh -V OK [join $ans \n]
 
     unsetenv_var TESTSUITE_ENABLE_SITECONFIG_TCLEXTLIBFAILEDMKTIME
-    unsetenv_var LD_PRELOAD
+    if {$tcl_platform(os) ne "Darwin"} {
+        unsetenv_var LD_PRELOAD
+    } else {
+        unsetenv_var DYLD_INSERT_LIBRARIES
+    }
 } elseif {$verbose} {
     send_user "\tSkip tcl ext lib erroneous procedure calls as mktime test lib is not available\n"
 }