Allow output of logging when running unit tests (#13556)

* Initial pass at enabling logging for unit tests

* Add to docs

* Bind debug for more test types

* Force everything

* Tidy up slightly

tests/test_common/main.cpp

@@ -0,0 +1,32 @@
+#include "gtest/gtest.h"
+
+extern "C" {
+#include "stdio.h"
+#include "debug.h"
+
+int8_t sendchar(uint8_t c) {
+    fprintf(stderr, "%c", c);
+    return 0;
+}
+
+__attribute__((weak)) debug_config_t debug_config = {0};
+
+void init_logging(void) {
+    print_set_sendchar(sendchar);
+
+    // Customise these values to desired behaviour
+    // debug_enable   = true;
+    // debug_matrix   = true;
+    // debug_keyboard = true;
+    // debug_mouse    = true;
+    debug_config.raw = 0xFF;
+}
+}
+
+int main(int argc, char **argv) {
+    ::testing::InitGoogleTest(&argc, argv);
+
+    init_logging();
+
+    return RUN_ALL_TESTS();
+}