test, string obfs: Add xor string obfuscator tests

test/impl/string_obfs.cpp

@@ -0,0 +1,16 @@
+#include <string_obfs.hpp>
+#include <catch2/catch.hpp>
+
+TEST_CASE("xor string obfs", "[StringObfs]") {
+    using byte = unsigned char;
+
+    auto xor = [](byte key) constexpr {
+        return [=](char c) constexpr -> char {
+            return c ^ key;
+        };
+    };
+
+    REQUIRE(
+        make_stringobfs("Hello World !", xor(0x20), xor(0x20)).decode()
+        == std::string_view("Hello World !"));
+}