diff --git a/utest/Makefile b/utest/Makefile
index 309538d..22bd8b8 100644
--- a/utest/Makefile
+++ b/utest/Makefile
@@ -19,8 +19,8 @@ SRC_DIR    = ../src
 UTEST_DIR  = ../utest
 VPATH      = $(SRC_DIR):$(SRC_DIR)/misc:$(UTEST_DIR)
 
-UTEST_NORM = global_mock.c bxstring_test.o cmdline_test.c tools_test.c regulex_test.o remove_test.o main.o \
-             unicode_test.o utest_tools.o
+UTEST_NORM = global_mock.c bxstring_test.o cmdline_test.c logging_test.c tools_test.c regulex_test.o remove_test.o \
+             main.o unicode_test.o utest_tools.o
 
 .PHONY: check_dir flags_unix flags_win32 flags_ utest
 
@@ -69,6 +69,7 @@ unittest.exe: $(UTEST_OBJ) | check_dir
 global_mock.o:   global_mock.c global_mock.h boxes.h unicode.h tools.h config.h | check_dir
 bxstring_test.o: bxstring_test.c bxstring_test.h boxes.h bxstring.h global_mock.h tools.h unicode.h utest_tools.h config.h | check_dir
 cmdline_test.o:  cmdline_test.c cmdline_test.h boxes.h cmdline.h global_mock.h tools.h config.h | check_dir
+logging_test.o:  logging_test.c logging_test.h boxes.h global_mock.h logging.h tools.h config.h | check_dir
 tools_test.o:    tools_test.c tools_test.h tools.h unicode.h config.h | check_dir
 regulex_test.o:  regulex_test.c regulex_test.h boxes.h global_mock.h regulex.h config.h | check_dir
 remove_test.o:   remove_test.c remove_test.h boxes.h remove.h shape.h tools.h unicode.h global_mock.h utest_tools.h config.h | check_dir
diff --git a/utest/logging_test.c b/utest/logging_test.c
new file mode 100644
index 0000000..7dd5b5f
--- /dev/null
+++ b/utest/logging_test.c
@@ -0,0 +1,252 @@
+/*
+ * boxes - Command line filter to draw/remove ASCII boxes around text
+ * Copyright (c) 1999-2024 Thomas Jensen and the boxes contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public
+ * License, version 3, as published by the Free Software Foundation.
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+ * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+ * details.
+ * You should have received a copy of the GNU General Public License along with this program.
+ * If not, see <https://www.gnu.org/licenses/>.
+ *
+* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ */
+
+/*
+ * Unit tests of the 'logging' module
+ */
+
+#include "config.h"
+
+#include <setjmp.h>
+#include <stdarg.h>
+#include <stddef.h>
+
+#include <cmocka.h>
+
+#include "boxes.h"
+#include "tools.h"
+#include "logging.h"
+#include "logging_test.h"
+#include "global_mock.h"
+#include "utest_tools.h"
+
+
+int logging_setup(void **state)
+{
+    UNUSED(state);
+
+    int *areas = (int *) calloc(NUM_LOG_AREAS, sizeof(int));
+    areas[MAIN - 2] = 1;
+    activate_debug_logging(areas);
+    BFREE(areas);
+    return 0;
+}
+
+
+
+int logging_teardown(void **state)
+{
+    UNUSED(state);
+
+    activate_debug_logging(NULL);  /* turn off debug logging */
+    return 0;
+}
+
+
+
+void test_debug_shorten_nopath(void **state)
+{
+    UNUSED(state);
+
+    log_debug("nopath.c", MAIN, "foo\n");
+
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("[nopath   ] foo\n", collect_err[0]);
+}
+
+
+
+void test_debug_shorten_minimal(void **state)
+{
+    UNUSED(state);
+
+    log_debug("minimal", MAIN, "foo\n");
+
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("[minimal  ] foo\n", collect_err[0]);
+}
+
+
+
+void test_debug_shorten_null(void **state)
+{
+    UNUSED(state);
+
+    log_debug(NULL, MAIN, "foo\n");
+
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("[NULL     ] foo\n", collect_err[0]);
+}
+
+
+
+void test_debug_shorten_backslash(void **state)
+{
+    UNUSED(state);
+
+    log_debug("..\\path\\to\\module.c", MAIN, "foo\n");
+
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("[module   ] foo\n", collect_err[0]);
+}
+
+
+
+void test_debug_shorten_slash(void **state)
+{
+    UNUSED(state);
+
+    log_debug("path/to/module.c", MAIN, "foo\n");
+
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("[module   ] foo\n", collect_err[0]);
+}
+
+
+
+void test_debug_shorten_nosuffix(void **state)
+{
+    UNUSED(state);
+
+    log_debug("path/to/module", MAIN, "foo\n");
+
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("[module   ] foo\n", collect_err[0]);
+}
+
+
+
+void test_debug_shorten_wrongdot(void **state)
+{
+    UNUSED(state);
+
+    log_debug("path/to.dot/module", MAIN, "foo\n");
+
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("[module   ] foo\n", collect_err[0]);
+}
+
+
+
+void test_debug_shorten_empty(void **state)
+{
+    UNUSED(state);
+
+    log_debug("", MAIN, "foo\n");
+
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("[         ] foo\n", collect_err[0]);
+}
+
+
+
+void test_debug_inactive_area(void **state)
+{
+    UNUSED(state);
+
+    log_debug("module.c", LEXER, "foo\n");
+
+    assert_int_equal(0, collect_err_size);
+}
+
+
+
+void test_debug_continue(void **state)
+{
+    UNUSED(state);
+
+    log_debug_cont(MAIN, "foo");
+
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("foo", collect_err[0]);
+}
+
+
+
+void test_debug_continue_inactive(void **state)
+{
+    UNUSED(state);
+
+    log_debug_cont(LEXER, "foo");
+
+    assert_int_equal(0, collect_err_size);
+}
+
+
+
+void test_debug_area_too_big(void **state)
+{
+    UNUSED(state);
+
+    log_debug("module.c", 100, "foo\n");  /* 100 is way too large and does not exist */
+
+    assert_int_equal(0, collect_err_size);
+}
+
+
+
+void test_debug_area_reserved(void **state)
+{
+    UNUSED(state);
+
+    log_debug("module.c", RESERVED, "foo\n");  /* RESERVED may never be used and is always "inactive" */
+
+    assert_int_equal(0, collect_err_size);
+}
+
+
+
+void test_debug_area_all(void **state)
+{
+    UNUSED(state);
+
+    log_debug("module.c", ALL, "foo\n");  /* only MAIN is active, but not all of them */
+
+    assert_int_equal(0, collect_err_size);
+}
+
+
+
+void test_debug_deactivated(void **state)
+{
+    UNUSED(state);
+
+    activate_debug_logging(NULL);
+    log_debug("module.c", MAIN, "foo\n");
+
+    assert_int_equal(0, collect_err_size);
+}
+
+
+
+void test_debug_all_active(void **state)
+{
+    UNUSED(state);
+
+    int *areas = (int *) calloc(NUM_LOG_AREAS, sizeof(int));
+    for(size_t i = 0; i < NUM_LOG_AREAS; i++) {
+        areas[i] = 1;
+    }
+    activate_debug_logging(areas);
+    BFREE(areas);
+
+    log_debug("module.c", ALL, "foo\n");
+
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("[module   ] foo\n", collect_err[0]);
+}
+
+
+/* vim: set cindent sw=4: */
diff --git a/utest/logging_test.h b/utest/logging_test.h
new file mode 100644
index 0000000..6813e92
--- /dev/null
+++ b/utest/logging_test.h
@@ -0,0 +1,49 @@
+/*
+ * boxes - Command line filter to draw/remove ASCII boxes around text
+ * Copyright (c) 1999-2024 Thomas Jensen and the boxes contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public
+ * License, version 3, as published by the Free Software Foundation.
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+ * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+ * details.
+ * You should have received a copy of the GNU General Public License along with this program.
+ * If not, see <https://www.gnu.org/licenses/>.
+ *
+* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ */
+
+/*
+ * Unit tests of the 'logging' module
+ */
+
+#ifndef LOGGING_TEST_H
+#define LOGGING_TEST_H
+
+#include "logging.h"
+
+int logging_setup(void **state);
+int logging_teardown(void **state);
+
+void test_debug_shorten_nopath(void **state);
+void test_debug_shorten_minimal(void **state);
+void test_debug_shorten_null(void **state);
+void test_debug_shorten_backslash(void **state);
+void test_debug_shorten_slash(void **state);
+void test_debug_shorten_nosuffix(void **state);
+void test_debug_shorten_wrongdot(void **state);
+void test_debug_shorten_empty(void **state);
+void test_debug_inactive_area(void **state);
+void test_debug_continue(void **state);
+void test_debug_continue_inactive(void **state);
+void test_debug_area_too_big(void **state);
+void test_debug_area_reserved(void **state);
+void test_debug_area_all(void **state);
+void test_debug_deactivated(void **state);
+void test_debug_all_active(void **state);
+
+
+#endif
+
+
+/* vim: set cindent sw=4: */
diff --git a/utest/main.c b/utest/main.c
index 8f836d7..60dfb3d 100644
--- a/utest/main.c
+++ b/utest/main.c
@@ -28,6 +28,7 @@
 #include "global_mock.h"
 #include "bxstring_test.h"
 #include "cmdline_test.h"
+#include "logging_test.h"
 #include "tools_test.h"
 #include "regulex_test.h"
 #include "remove_test.h"
@@ -218,6 +219,24 @@ int main(void)
         cmocka_unit_test_setup(test_hmm_blank, beforeTest)
     };
 
+    const struct CMUnitTest logging_tests[] = {
+        cmocka_unit_test_setup(test_debug_shorten_nopath, beforeTest),
+        cmocka_unit_test_setup(test_debug_shorten_minimal, beforeTest),
+        cmocka_unit_test_setup(test_debug_shorten_null, beforeTest),
+        cmocka_unit_test_setup(test_debug_shorten_backslash, beforeTest),
+        cmocka_unit_test_setup(test_debug_shorten_slash, beforeTest),
+        cmocka_unit_test_setup(test_debug_shorten_nosuffix, beforeTest),
+        cmocka_unit_test_setup(test_debug_shorten_wrongdot, beforeTest),
+        cmocka_unit_test_setup(test_debug_shorten_empty, beforeTest),
+        cmocka_unit_test_setup(test_debug_inactive_area, beforeTest),
+        cmocka_unit_test_setup(test_debug_continue, beforeTest),
+        cmocka_unit_test_setup(test_debug_continue_inactive, beforeTest),
+        cmocka_unit_test_setup(test_debug_area_too_big, beforeTest),
+        cmocka_unit_test_setup(test_debug_area_reserved, beforeTest),
+        cmocka_unit_test_setup(test_debug_area_all, beforeTest),
+        cmocka_unit_test_setup(test_debug_deactivated, beforeTest),
+        cmocka_unit_test_setup(test_debug_all_active, beforeTest)
+    };
 
     int num_failed = 0;
     num_failed += cmocka_run_group_tests(cmdline_tests, NULL, NULL);
@@ -226,6 +245,7 @@ int main(void)
     num_failed += cmocka_run_group_tests(unicode_tests, NULL, NULL);
     num_failed += cmocka_run_group_tests(bxstring_tests, NULL, NULL);
     num_failed += cmocka_run_group_tests(remove_tests, NULL, NULL);
+    num_failed += cmocka_run_group_tests(logging_tests, logging_setup, logging_teardown);
 
     teardown();
     return num_failed;