diff --git a/.gitmodules b/.gitmodules
index 5c918c1..05929b2 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -199,3 +199,6 @@
 [submodule "third_party/spdlog"]
 	path = third_party/spdlog
 	url = https://github.com/gabime/spdlog
+[submodule "third_party/catch2"]
+	path = third_party/catch2
+	url = https://github.com/catchorg/Catch2
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5a11d4d..47d4b5f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -15,6 +15,8 @@ include(Policies)
 include(ProjectFuncs)
 include(CompilerFlags)
 
+option(LS_BUILD_TESTING "Build unit tests" ON)
+
 lobbyserver_set_alternate_linker()
 
 # third party vendor dependencies
diff --git a/lib/aries/Tags.cpp b/lib/aries/Tags.cpp
index a34643a..b619da9 100644
--- a/lib/aries/Tags.cpp
+++ b/lib/aries/Tags.cpp
@@ -98,4 +98,20 @@ namespace ls::aries {
 
 		outStr = std::move(tagFieldBuffer);
 	}
+
+	std::vector<u8> DecodeBinaryTagData(std::string_view tagData) {
+		// This could be more ergonomic as an optional or something.
+
+		if(tagData.empty())
+			return {};
+
+		// Marker for binary data
+		if(tagData[0] != '$')
+			return {};
+
+		// TODO: Implement me fully!
+
+		return {};
+	}
+
 } // namespace ls::aries
\ No newline at end of file
diff --git a/lib/aries/Tags.hpp b/lib/aries/Tags.hpp
index a6cebfe..9782783 100644
--- a/lib/aries/Tags.hpp
+++ b/lib/aries/Tags.hpp
@@ -14,4 +14,11 @@ namespace ls::aries {
     /// Serializes a TagMap to a string.
     void SerializeTagFields(const TagMap& map, std::string& outStr);
 
+    /// Decodes a binary tag to binary data.
+    std::vector<u8> DecodeBinaryTagData(std::string_view tagData);
+
+    
+    // TODO: Maybe also a in-Aries implementation of "CryptoSSC2"/other dirtysock crypto primitives so that we can rehash
+    // passwords to an actually sane password hash (e.g: argon2di).
+
 }
\ No newline at end of file
diff --git a/lib/aries/Tags.test.cpp b/lib/aries/Tags.test.cpp
new file mode 100644
index 0000000..e765b23
--- /dev/null
+++ b/lib/aries/Tags.test.cpp
@@ -0,0 +1,34 @@
+#include <aries/Tags.hpp>
+#include <catch2/catch_all.hpp>
+namespace aries = ls::aries;
+
+TEST_CASE("Aries tag field serde functions as expected", "[Aries] [TagFields]") {
+	const static aries::TagMap expectedMap = {
+		{ "PROP1", "VAL1" },
+		{ "PROP2", "VAL2" },
+		{ "PROP3", "VAL3" },
+		{ "PROP4", "VAL4" },
+	};
+
+	std::string validTagBuffer;
+
+	SECTION("Serialization works as expected") {
+		// Do the serialization and make sure it's valid
+		aries::SerializeTagFields(expectedMap, validTagBuffer);
+		REQUIRE(validTagBuffer == "PROP4=VAL4\nPROP3=VAL3\nPROP2=VAL2\nPROP1=VAL1\n");
+	}
+
+	// For some obscure reason this can't be in a SECTION
+	// (maybe I'll try boost-ext/ut again if this becomes more frequent..)
+	aries::TagMap deserializedMap;
+	REQUIRE(aries::ParseTagFieldsToMap(validTagBuffer, deserializedMap) != false);
+	REQUIRE(deserializedMap == expectedMap);
+}
+
+TEST_CASE("DecodeBinaryTagData() works", "[Aries] [TagFields] [DecodeBinarytagData]") {
+	// should decode to [ 0x12, 0x34, 0x56, 0x78 ]
+	std::string testCorpus = "$12345678";
+	const static std::vector<u8> expectedOutput = { 0x12, 0x34, 0x56, 0x78 };
+
+    REQUIRE(aries::DecodeBinaryTagData(testCorpus) == expectedOutput);
+}
\ No newline at end of file
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index b216733..3507e60 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -21,3 +21,23 @@ target_link_libraries(lobbyserver PRIVATE
 	Boost::json
 	ls::aries
 )
+
+# == unit test driver ==
+if(LS_BUILD_TESTING)
+
+	add_executable(testdriver
+		# this is a bit :( 
+		../lib/aries/Tags.test.cpp
+	)
+
+	lobbyserver_target(testdriver)
+
+	target_link_libraries(testdriver
+		Catch2::Catch2WithMain
+
+		ls::aries
+	)
+
+	# TODO: CTest integration
+
+endif()
\ No newline at end of file
diff --git a/third_party/CMakeLists.txt b/third_party/CMakeLists.txt
index f3b4534..e90dbdd 100644
--- a/third_party/CMakeLists.txt
+++ b/third_party/CMakeLists.txt
@@ -2,4 +2,8 @@ add_subdirectory(boost)
 add_subdirectory(tomlplusplus)
 
 set(SPDLOG_USE_STD_FORMAT ON)
-add_subdirectory(spdlog)
\ No newline at end of file
+add_subdirectory(spdlog)
+
+if(LS_BUILD_TESTING)
+    add_subdirectory(catch2)
+endif()
\ No newline at end of file
diff --git a/third_party/catch2 b/third_party/catch2
new file mode 160000
index 0000000..8ac8190
--- /dev/null
+++ b/third_party/catch2
@@ -0,0 +1 @@
+Subproject commit 8ac8190e494a381072c89f5e161b92a08d98b37b