diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 26992fd..65f1d5c 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -2,6 +2,7 @@ image: gcc
 
 stages:
   - build
+  - test
 
 build:
   stage: build
@@ -10,3 +11,9 @@ build:
   artifacts:
     paths:
       - main
+  stage: test
+
+unit-testing:
+  stage: test
+  script:
+    - make unit-tests
diff --git a/Makefile b/Makefile
index 70e2adb..87b974a 100644
--- a/Makefile
+++ b/Makefile
@@ -1,18 +1,25 @@
 MAKEFLAGS="-j $(grep -c ^processor /proc/cpuinfo)"
 CXXFLAGS=-std=c++20 -Wall -Wextra -O2 -Werror=switch
-CPPFLAGS=-Ilib/expected/ -Ilib/ut/
+CPPFLAGS=-Ilib/expected/ -Ilib/ut/ -Isrc/
 
 Obj=bin/lexer.o \
-		bin/errors.o \
-		bin/main.o
+		bin/errors.o
+
+all: bin/musique bin/unit-tests
 
-all: bin/musique
 
 bin/%.o: src/%.cc src/*.hh
 	g++ $(CXXFLAGS) $(CPPFLAGS) -o $@ $< -c
 
-bin/musique: $(Obj) src/*.hh
-	g++ $(CXXFLAGS) $(CPPFLAGS) -o $@ $(Obj)
+bin/musique: $(Obj) bin/main.o src/*.hh
+	g++ $(CXXFLAGS) $(CPPFLAGS) -o $@ $(Obj) bin/main.o
+
+.PHONY: unit-tests
+unit-tests: bin/unit-tests
+	./$<
+
+bin/unit-tests: src/tests/*.cc $(Obj)
+	g++ $(CXXFLAGS) $(CPPFLAGS) -o $@ $^
 
 clean:
 	rm -rf bin
diff --git a/src/errors.cc b/src/errors.cc
index 4ff2a1b..7971abe 100644
--- a/src/errors.cc
+++ b/src/errors.cc
@@ -1,4 +1,9 @@
-#include "musique.hh"
+#include <musique.hh>
+
+bool Error::operator==(errors::Type type)
+{
+	return this->type == type;
+}
 
 std::ostream& operator<<(std::ostream& os, Error const&)
 {
diff --git a/src/lexer.cc b/src/lexer.cc
index c4892c1..3311889 100644
--- a/src/lexer.cc
+++ b/src/lexer.cc
@@ -1,4 +1,4 @@
-#include "musique.hh"
+#include <musique.hh>
 
 auto Lexer::next_token() -> Result<Token>
 {
diff --git a/src/main.cc b/src/main.cc
index 483a36d..a0c9835 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -1,5 +1,5 @@
 #include <iostream>
-#include "musique.hh"
+#include <musique.hh>
 
 std::string_view Source = R"musique(
 	nums = [ 1 2 3 ]
diff --git a/src/musique.hh b/src/musique.hh
index 832248b..6314d16 100644
--- a/src/musique.hh
+++ b/src/musique.hh
@@ -15,10 +15,21 @@ using i16 = std::int16_t;
 using i32 = std::int32_t;
 using i64 = std::int64_t;
 
+
+namespace errors
+{
+	enum Type
+	{
+		End_Of_File
+	};
+}
+
 struct Error
 {
-	std::string_view message;
+	errors::Type type;
 	Error *child = nullptr;
+
+	bool operator==(errors::Type);
 };
 
 template<typename T>
@@ -59,6 +70,7 @@ struct Token
 		Close_Paren
 	};
 
+	Type type;
 	std::string_view source;
 };
 
diff --git a/src/tests/lex.cc b/src/tests/lex.cc
new file mode 100644
index 0000000..636c455
--- /dev/null
+++ b/src/tests/lex.cc
@@ -0,0 +1,57 @@
+#include <boost/ut.hpp>
+#include <musique.hh>
+
+using namespace boost::ut;
+
+auto under(auto enumeration) requires std::is_enum_v<decltype(enumeration)>
+{
+	return static_cast<std::underlying_type_t<decltype(enumeration)>>(enumeration);
+}
+
+static void expect_token_type(
+		Token::Type expected_type,
+		std::string source,
+		reflection::source_location const& sl = reflection::source_location::current())
+{
+	Lexer lexer{source};
+	auto result = lexer.next_token();
+	expect(result.has_value() >> fatal, sl) << "have not parsed any tokens";
+	expect(eq(under(result->type), under(expected_type)), sl) << "different token type then expected";
+}
+
+static void expect_token_type_and_value(
+		Token::Type expected_type,
+		std::string_view source,
+		reflection::source_location const& sl = reflection::source_location::current())
+{
+	Lexer lexer{source};
+	auto result = lexer.next_token();
+	expect(result.has_value() >> fatal, sl) << "have not parsed any tokens";
+	expect(eq(under(result->type), under(expected_type)), sl) << "different token type then expected";
+	expect(eq(result->source, source)) << "tokenized source is not equal to original";
+}
+
+suite lexer_test = [] {
+	"Empty file"_test = [] {
+		Lexer lexer{""};
+		auto result = lexer.next_token();
+		expect(!result.has_value() >> fatal) << "could not produce any tokens from empty file";
+		expect(result.error() == errors::End_Of_File) << "could not produce any tokens from empty file";
+	};
+
+	"Simple token types"_test = [] {
+		expect_token_type(Token::Type::Close_Block,        "]");
+		expect_token_type(Token::Type::Close_Paren,        ")");
+		expect_token_type(Token::Type::Open_Block,         "[");
+		expect_token_type(Token::Type::Open_Paren,         "(");
+		expect_token_type(Token::Type::Variable_Separator, "|");
+	};
+
+	"Numeric tokens"_test = [] {
+		expect_token_type_and_value(Token::Type::Numeric, "0");
+		expect_token_type_and_value(Token::Type::Numeric, "123456789");
+		expect_token_type_and_value(Token::Type::Numeric, ".75");
+		expect_token_type_and_value(Token::Type::Numeric, "0.75");
+		expect_token_type_and_value(Token::Type::Numeric, "123456789.123456789");
+	};
+};
diff --git a/src/tests/main.cc b/src/tests/main.cc
new file mode 100644
index 0000000..784aabe
--- /dev/null
+++ b/src/tests/main.cc
@@ -0,0 +1,12 @@
+#include <boost/ut.hpp>
+
+int main()
+{
+	using namespace boost::ut;
+
+	if (!isatty(STDOUT_FILENO)) {
+		cfg<override> = options {
+			.colors = colors { .none = "", .pass = "", .fail = "" }
+		};
+	}
+}