Move tests to relevant subprojects (#615)

- Moved test projects to the parent project they belong to
- Improved test stability/corectness
- Improved recursive directory deletion by safely ignoring current- and parent-directory entries.
- Update docs

TactilityKernel/tests/source/paths_test.cpp

@@ -0,0 +1,31 @@
+#include "doctest.h"
+
+#include <cstring>
+
+#include <tactility/paths.h>
+
+// The simulator target is never built with ESP_PLATFORM, so paths_get_user_data_path()
+// always takes the fixed "data" path branch here, guarded by a buffer-size check.
+
+TEST_CASE("paths_get_user_data_path succeeds when the buffer exactly fits") {
+    char buffer[16] = { 0 };
+    CHECK_EQ(paths_get_user_data_path(buffer, sizeof(buffer)), ERROR_NONE);
+    CHECK_EQ(std::strcmp(buffer, "data"), 0);
+}
+
+TEST_CASE("paths_get_user_data_path succeeds with a buffer sized to exactly fit the string and terminator") {
+    char buffer[5] = { 0 }; // strlen("data") + 1
+    CHECK_EQ(paths_get_user_data_path(buffer, sizeof(buffer)), ERROR_NONE);
+    CHECK_EQ(std::strcmp(buffer, "data"), 0);
+}
+
+TEST_CASE("paths_get_user_data_path reports a buffer overflow when the buffer is one byte too small") {
+    char buffer[4] = { 0 }; // strlen("data"), no room for the terminator
+    CHECK_EQ(paths_get_user_data_path(buffer, sizeof(buffer)), ERROR_BUFFER_OVERFLOW);
+}
+
+TEST_CASE("paths_get_user_data_path reports a buffer overflow for a zero-size buffer") {
+    char buffer[1] = { 'x' };
+    CHECK_EQ(paths_get_user_data_path(buffer, 0), ERROR_BUFFER_OVERFLOW);
+    CHECK_EQ(buffer[0], 'x'); // untouched
+}