Move tests from projects/ to tests/

tests/ExtraTests/X10-FallbackStringifier.cpp

@@ -0,0 +1,23 @@
+// X10-FallbackStringifier.cpp
+// Test that defining fallbackStringifier compiles
+
+#include <string>
+
+// A catch-all stringifier
+template <typename T>
+std::string fallbackStringifier(T const&) {
+    return "{ !!! }";
+}
+
+#define CATCH_CONFIG_MAIN
+#include <catch2/catch.hpp>
+
+struct foo {
+    explicit operator bool() const {
+        return true;
+    }
+};
+
+TEST_CASE("aa") {
+    REQUIRE(foo{});
+}