diff --git a/src/regulex.c b/src/regulex.c
index 66855e1..34947f8 100644
--- a/src/regulex.c
+++ b/src/regulex.c
@@ -55,7 +55,7 @@ pcre2_code *compile_pattern(char *pattern)
     if (re == NULL) {
         PCRE2_UCHAR buffer[256];
         pcre2_get_error_message(errornumber, buffer, sizeof(buffer));
-        fprintf(stderr, "Regular expression pattern \"%s\" failed to compile at offset %d: %s\n",
+        fprintf(stderr, "Regular expression pattern \"%s\" failed to compile at position %d: %s\n",
                 pattern, (int) erroroffset, u32_strconv_to_output(buffer));
     }
     return re;
diff --git a/utest/Makefile b/utest/Makefile
index ee4dc34..53ee963 100644
--- a/utest/Makefile
+++ b/utest/Makefile
@@ -24,7 +24,8 @@ SRC_DIR    = ../src
 UTEST_DIR  = ../utest
 VPATH      = $(SRC_DIR):$(SRC_DIR)/misc:$(UTEST_DIR)
 
-UTEST_NORM = global_mock.c tools_test.c
+UTEST_NORM = global_mock.c tools_test.c regulex_test.o main.o
+MOCKS = fprintf
 
 .PHONY: check_dir flags_unix flags_win32 flags_ utest
 
@@ -41,13 +42,13 @@ $(OUT_DIR):
 
 flags_unix:
 	$(eval CFLAGS := -I. -I$(SRC_DIR) -O -Wall -W $(CFLAGS_ADDTL))
-	$(eval LDFLAGS := $(LDFLAGS) --coverage $(LDFLAGS_ADDTL))
+	$(eval LDFLAGS := $(LDFLAGS) $(foreach MOCK,$(MOCKS),-Wl,--wrap=$(MOCK)) --coverage $(LDFLAGS_ADDTL))
 	$(eval UTEST_EXECUTABLE_NAME := unittest)
 	$(eval UTEST_OBJ := $(UTEST_NORM:.c=.o))
 
 flags_win32:
 	$(eval CFLAGS := -Os -s -m32 -I. -I$(SRC_DIR) -Wall -W $(CFLAGS_ADDTL))
-	$(eval LDFLAGS := $(LDFLAGS) --coverage -s -m32 $(LDFLAGS_ADDTL))
+	$(eval LDFLAGS := $(LDFLAGS) $(foreach MOCK,$(MOCKS),-Wl,--wrap=$(MOCK)) --coverage -s -m32 $(LDFLAGS_ADDTL))
 	$(eval UTEST_EXECUTABLE_NAME := unittest.exe)
 	$(eval UTEST_OBJ := $(UTEST_NORM:.c=.o))
 
@@ -70,5 +71,7 @@ unittest.exe: $(UTEST_OBJ) | check_dir
 	    -lkernel32 -l:libunistring.a -l:libpcre2-32.a -l:libiconv.a -l:libcmocka.dll.a
 
 
-global_mock.o: global_mock.c boxes.h
-tools_test.o: tools_test.c tools.h
+global_mock.o:  global_mock.c global_mock.h boxes.h unicode.h config.h | check_dir
+tools_test.o:   tools_test.c tools_test.h tools.h config.h | check_dir
+regulex_test.o: regulex_test.c regulex_test.h global_mock.h regulex.h config.h | check_dir
+main.o:         main.c global_mock.h tools_test.h regulex_test.h config.h | check_dir
diff --git a/utest/global_mock.c b/utest/global_mock.c
index 6ae3375..55624ce 100644
--- a/utest/global_mock.c
+++ b/utest/global_mock.c
@@ -22,8 +22,15 @@
  * Mocks of boxes' global variables.
  */
 
+#include "config.h"
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+#include <locale.h>
+#include <uniconv.h>
 #include "boxes.h"
-
+#include "unicode.h"
+#include "tools.h"
 
 design_t *designs = NULL;
 
@@ -32,3 +39,73 @@ int num_designs = 0;
 opt_t opt;
 
 input_t input;
+
+char **collect_out = NULL;
+int collect_out_size = 0;
+
+char **collect_err = NULL;
+int collect_err_size = 0;
+
+
+void collect_reset()
+{
+    for (int i = 0; i < collect_out_size; i++) {
+        BFREE(collect_out[i]);
+    }
+    BFREE(collect_out);
+
+    for (int i = 0; i < collect_err_size; i++) {
+        BFREE(collect_err[i]);
+    }
+    BFREE(collect_err);
+
+    collect_out_size = 0;
+    collect_err_size = 0;
+}
+
+
+/**
+ * Mock of the `fprintf()` function which records its output instead of printing it. Assumes that no output string will
+ * be longer than 512 characters.
+ * @param __stream `stdout` or `stderr`
+ * @param __format the format string, followed by the arguments
+ */
+void __wrap_fprintf(FILE *__stream, const char *__format, ...)
+{
+    char **collect = __stream == stdout ? collect_out : collect_err;
+    int collect_size = __stream == stdout ? collect_out_size : collect_err_size;
+    collect = (char **) realloc(collect, ++collect_size * sizeof(char *));
+
+    char *s = (char *) malloc(512);
+    va_list va;
+    va_start(va, __format);
+    vsprintf(s, __format, va);
+    va_end(va);
+    collect[collect_size - 1] = s;
+
+    if (__stream == stdout) {
+        collect_out = collect;
+        collect_out_size = collect_size;
+    }
+    else {
+        collect_err = collect;
+        collect_err_size = collect_size;
+    }
+}
+
+
+void setup_mocks()
+{
+    setlocale(LC_ALL, "");
+    encoding = check_encoding("UTF-8", locale_charset());
+    collect_reset();
+}
+
+
+void teardown()
+{
+    collect_reset();
+}
+
+
+/*EOF*/                                          /* vim: set cindent sw=4: */
diff --git a/utest/global_mock.h b/utest/global_mock.h
new file mode 100644
index 0000000..1cb304b
--- /dev/null
+++ b/utest/global_mock.h
@@ -0,0 +1,44 @@
+/*
+ * boxes - Command line filter to draw/remove ASCII boxes around text
+ * Copyright (c) 1999-2021 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 2, 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ */
+
+/*
+ * Test fixtures and mocks of global shared state.
+ */
+
+#ifndef GLOBAL_MOCK_H
+#define GLOBAL_MOCK_H
+
+
+extern char **collect_out;
+extern int collect_out_size;
+
+extern char **collect_err;
+extern int collect_err_size;
+
+void collect_reset();
+
+
+void setup_mocks();
+void teardown();
+
+
+#endif
+
+/*EOF*/                                          /* vim: set cindent sw=4: */
diff --git a/utest/main.c b/utest/main.c
new file mode 100644
index 0000000..575befa
--- /dev/null
+++ b/utest/main.c
@@ -0,0 +1,61 @@
+/*
+ * boxes - Command line filter to draw/remove ASCII boxes around text
+ * Copyright (c) 1999-2021 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 2, 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ */
+
+/*
+ * Main module for running the unit tests.
+ */
+
+#include "config.h"
+#include <stdarg.h>
+#include <stddef.h>
+#include <setjmp.h>
+#include <cmocka.h>
+
+#include "global_mock.h"
+#include "tools_test.h"
+#include "regulex_test.h"
+
+
+int main(void)
+{
+    setup_mocks();
+
+    const struct CMUnitTest tools_tests[] = {
+        cmocka_unit_test(test_strisyes_true),
+        cmocka_unit_test(test_strisyes_false),
+        cmocka_unit_test(test_strisno_true),
+        cmocka_unit_test(test_strisno_false)
+    };
+
+    const struct CMUnitTest regulex_tests[] = {
+        cmocka_unit_test(test_compile_pattern_error),
+        cmocka_unit_test(test_compile_pattern_empty)
+    };
+
+    int num_failed = 0;
+    num_failed += cmocka_run_group_tests(tools_tests, NULL, NULL);
+    num_failed += cmocka_run_group_tests(regulex_tests, NULL, NULL);
+
+    teardown();
+    return num_failed;
+}
+
+
+/*EOF*/                                          /* vim: set cindent sw=4: */
diff --git a/utest/regulex_test.c b/utest/regulex_test.c
new file mode 100644
index 0000000..b676b6e
--- /dev/null
+++ b/utest/regulex_test.c
@@ -0,0 +1,60 @@
+/*
+ * boxes - Command line filter to draw/remove ASCII boxes around text
+ * Copyright (c) 1999-2021 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 2, 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ */
+
+/*
+ * Unit tests of the 'regulex' module
+ */
+
+#include "config.h"
+#include <stdarg.h>
+#include <stddef.h>
+#include <setjmp.h>
+#include <cmocka.h>
+#include "global_mock.h"
+#include "regulex.h"
+
+
+void test_compile_pattern_empty(void **state)
+{
+    (void) state;  /* unused */
+
+    assert_null(compile_pattern(NULL));
+    assert_non_null(compile_pattern(""));
+}
+
+
+void test_compile_pattern_error(void **state)
+{
+    (void) state;  /* unused */
+
+    assert_null(compile_pattern("incomplete[x"));
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("Regular expression pattern \"incomplete[x\" failed to compile at position 12: "
+        "missing terminating ] for character class\n", collect_err[0]);
+
+    collect_reset();
+    assert_null(compile_pattern("incomplete\\"));
+    assert_int_equal(1, collect_err_size);
+    assert_string_equal("Regular expression pattern \"incomplete\\\" failed to compile at position 11: "
+        "\\ at end of pattern\n", collect_err[0]);
+}
+
+
+/*EOF*/                                          /* vim: set cindent sw=4: */
diff --git a/utest/regulex_test.h b/utest/regulex_test.h
new file mode 100644
index 0000000..cd6fc88
--- /dev/null
+++ b/utest/regulex_test.h
@@ -0,0 +1,36 @@
+/*
+ * boxes - Command line filter to draw/remove ASCII boxes around text
+ * Copyright (c) 1999-2021 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 2, 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ */
+
+/*
+ * Unit tests of the 'regulex' module
+ */
+
+#ifndef REGULEX_TEST_H
+#define REGULEX_TEST_H
+
+
+void test_compile_pattern_empty(void **state);
+void test_compile_pattern_error(void **state);
+
+
+#endif
+
+
+/*EOF*/                                          /* vim: set cindent sw=4: */
diff --git a/utest/tools_test.c b/utest/tools_test.c
index 98bf533..cfe71c9 100644
--- a/utest/tools_test.c
+++ b/utest/tools_test.c
@@ -22,15 +22,19 @@
  * Unit tests of the 'tools' module
  */
 
+#include "config.h"
 #include <stdarg.h>
 #include <stddef.h>
 #include <setjmp.h>
 #include <cmocka.h>
 #include "tools.h"
+#include "tools_test.h"
 
 
-static void test_strisyes_true()
+void test_strisyes_true(void **state)
 {
+    (void) state;  /* unused */
+
     assert_int_equal(1, strisyes("On"));
     assert_int_equal(1, strisyes("on"));
     assert_int_equal(1, strisyes("yes"));
@@ -43,8 +47,10 @@ static void test_strisyes_true()
 }
 
 
-static void test_strisyes_false()
+void test_strisyes_false(void **state)
 {
+    (void) state;  /* unused */
+
     assert_int_equal(0, strisyes(NULL));
     assert_int_equal(0, strisyes(""));
     assert_int_equal(0, strisyes(" "));
@@ -60,8 +66,10 @@ static void test_strisyes_false()
 }
 
 
-static void test_strisno_true()
+void test_strisno_true(void **state)
 {
+    (void) state;  /* unused */
+
     assert_int_equal(1, strisno("off"));
     assert_int_equal(1, strisno("Off"));
     assert_int_equal(1, strisno("no"));
@@ -74,8 +82,10 @@ static void test_strisno_true()
 }
 
 
-static void test_strisno_false()
+void test_strisno_false(void **state)
 {
+    (void) state;  /* unused */
+
     assert_int_equal(0, strisno(NULL));
     assert_int_equal(0, strisno(""));
     assert_int_equal(0, strisno(" "));
@@ -91,14 +101,4 @@ static void test_strisno_false()
 }
 
 
-int main(void)
-{
-    const struct CMUnitTest tests[] = {
-        cmocka_unit_test(test_strisyes_true),
-        cmocka_unit_test(test_strisyes_false),
-        cmocka_unit_test(test_strisno_true),
-        cmocka_unit_test(test_strisno_false)
-    };
-
-    return cmocka_run_group_tests(tests, NULL, NULL);
-}
+/*EOF*/                                          /* vim: set cindent sw=4: */
diff --git a/utest/tools_test.h b/utest/tools_test.h
new file mode 100644
index 0000000..26e4058
--- /dev/null
+++ b/utest/tools_test.h
@@ -0,0 +1,38 @@
+/*
+ * boxes - Command line filter to draw/remove ASCII boxes around text
+ * Copyright (c) 1999-2021 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 2, 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, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ */
+
+/*
+ * Unit tests of the 'tools' module
+ */
+
+#ifndef TOOLS_TEST_H
+#define TOOLS_TEST_H
+
+
+void test_strisyes_true(void **state);
+void test_strisyes_false(void **state);
+
+void test_strisno_true(void **state);
+void test_strisno_false(void **state);
+
+
+#endif
+
+/*EOF*/                                          /* vim: set cindent sw=4: */