[client] tests: add stb font compatibility coverage

client/tests/CMakeLists.txt

@@ -1,5 +1,22 @@
 cmake_minimum_required(VERSION 3.10)
 
+add_executable(font-tests
+  font_test.c
+  ../src/font.c
+)
+target_compile_definitions(font-tests PRIVATE
+  FONT_TEST_FILE="${PROJECT_TOP}/repos/cimgui/imgui/misc/fonts/DroidSans.ttf"
+)
+target_include_directories(font-tests PRIVATE
+  "${CMAKE_CURRENT_SOURCE_DIR}/../include"
+)
+add_test(NAME font-tests
+  COMMAND font-tests
+)
+set_tests_properties(font-tests PROPERTIES
+  TIMEOUT 10
+)
+
 if(ENABLE_TRANSPORT_TESTS)
   add_executable(lgmp-transport-tests
     lgmp_transport_test.c

client/tests/font_test.c

@@ -0,0 +1,67 @@
+/**
+ * Looking Glass
+ * Copyright © 2017-2026 The Looking Glass Authors
+ * https://looking-glass.io
+ *
+ * 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 the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * 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., 59
+ * Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include "font.h"
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static void testInvalidFontData(void)
+{
+  const unsigned char emptySfnt[12] = {
+    0x00, 0x01, 0x00, 0x00,
+  };
+  assert(!font_isStbTruetypeCompatible(
+        emptySfnt, sizeof(emptySfnt), 0));
+
+  const unsigned char truncatedTableDirectory[12] = {
+    0x00, 0x01, 0x00, 0x00,
+    0x00, 0x01,
+  };
+  assert(!font_isStbTruetypeCompatible(
+        truncatedTableDirectory, sizeof(truncatedTableDirectory), 0));
+}
+
+static void testValidFontData(void)
+{
+  FILE * file = fopen(FONT_TEST_FILE, "rb");
+  assert(file);
+  assert(fseek(file, 0, SEEK_END) == 0);
+  const long length = ftell(file);
+  assert(length > 0);
+  assert(fseek(file, 0, SEEK_SET) == 0);
+
+  void * data = malloc((size_t)length);
+  assert(data);
+  assert(fread(data, 1, (size_t)length, file) == (size_t)length);
+  assert(fclose(file) == 0);
+
+  assert(font_isStbTruetypeCompatible(data, (size_t)length, 0));
+  assert(!font_isStbTruetypeCompatible(data, (size_t)length, 1));
+  free(data);
+}
+
+int main(void)
+{
+  testInvalidFontData();
+  testValidFontData();
+  return 0;
+}