diff --git a/.gitea/workflows/build.yml b/.gitea/workflows/test.yml
similarity index 81%
rename from .gitea/workflows/build.yml
rename to .gitea/workflows/test.yml
index cbc8480..cf4cb0b 100644
--- a/.gitea/workflows/build.yml
+++ b/.gitea/workflows/test.yml
@@ -1,4 +1,4 @@
-name: Build
+name: Test
 
 on: push
 
@@ -12,3 +12,5 @@ jobs:
         run: cmake -S emulator -B emulator/build
       - name: Build
         run: cmake --build emulator/build
+      - name: Test
+        ctest emulator/build
diff --git a/emulator/CMakeLists.txt b/emulator/CMakeLists.txt
index abcebcd..bef228e 100644
--- a/emulator/CMakeLists.txt
+++ b/emulator/CMakeLists.txt
@@ -1,5 +1,14 @@
 cmake_minimum_required(VERSION 3.20)
 
-project(foot-emu)
+project(foot-emulator)
 
-add_executable(foot-emu main.cpp foot-emulator.cpp foot-emulator.h)
+add_library(foot-emulator src/foot-emulator.cpp include/foot-emulator.h)
+target_include_directories(foot-emulator PUBLIC include)
+
+add_executable(foot-emulator-cli src/main.cpp)
+target_link_libraries(foot-emulator-cli PUBLIC foot-emulator)
+
+if(PROJECT_IS_TOP_LEVEL)
+  enable_testing()
+  add_subdirectory(tests)
+endif()
diff --git a/emulator/foot-emulator.h b/emulator/include/foot-emulator.h
similarity index 97%
rename from emulator/foot-emulator.h
rename to emulator/include/foot-emulator.h
index b97a5a3..e1c2373 100644
--- a/emulator/foot-emulator.h
+++ b/emulator/include/foot-emulator.h
@@ -59,6 +59,9 @@ public:
 
   uint16_t& memory_at(uint16_t address);
   uint16_t& decode_operand(Operand operand);
+  uint16_t& register_at(uint8_t index);
+
+  void run_instruction();
 
 private:
   std::array<uint16_t, 1 << 16> memory;
@@ -76,7 +79,6 @@ private:
   uint16_t mapped_base;
 
   void read_instruction();
-  void run_instruction();
 
   void CNST();
   void CMPR();
diff --git a/emulator/foot-emulator.cpp b/emulator/src/foot-emulator.cpp
similarity index 98%
rename from emulator/foot-emulator.cpp
rename to emulator/src/foot-emulator.cpp
index 773307d..8858e65 100644
--- a/emulator/foot-emulator.cpp
+++ b/emulator/src/foot-emulator.cpp
@@ -91,12 +91,9 @@ uint16_t& Emulator::decode_operand(Operand operand)
   }
 }
 
-void Emulator::read_instruction()
+uint16_t& Emulator::register_at(uint8_t index)
 {
-  uint16_t low  = memory[registers[PC]++];
-  uint16_t high = memory[registers[PC]++];
-
-  instruction = (uint32_t(high) << 16) | uint32_t(low);
+  return registers[index];
 }
 
 void Emulator::run_instruction()
@@ -197,6 +194,14 @@ void Emulator::run_instruction()
   if (rep) { registers[LC] = loop_count; }
 }
 
+void Emulator::read_instruction()
+{
+  uint16_t low  = memory[registers[PC]++];
+  uint16_t high = memory[registers[PC]++];
+
+  instruction = (uint32_t(high) << 16) | uint32_t(low);
+}
+
 void Emulator::CNST()
 {
   decode_operand((instruction & 0x00FF0000) >> 16) = instruction & 0x0000FFFF;
diff --git a/emulator/main.cpp b/emulator/src/main.cpp
similarity index 100%
rename from emulator/main.cpp
rename to emulator/src/main.cpp
diff --git a/emulator/tests/CMakeLists.txt b/emulator/tests/CMakeLists.txt
new file mode 100644
index 0000000..dc68f0e
--- /dev/null
+++ b/emulator/tests/CMakeLists.txt
@@ -0,0 +1,11 @@
+cmake_minimum_required(VERSION 3.20)
+
+include(CTest)
+
+function(test name)
+  add_executable(foot-emulator-test-${name} ${name}.cpp test-common.h)
+  target_link_libraries(foot-emulator-test-${name} PUBLIC foot-emulator)
+  add_test(NAME ${name} COMMAND foot-emulator-test-${name})
+endfunction()
+
+test(cnst-instruction)
diff --git a/emulator/tests/cnst-instruction.cpp b/emulator/tests/cnst-instruction.cpp
new file mode 100644
index 0000000..c68abac
--- /dev/null
+++ b/emulator/tests/cnst-instruction.cpp
@@ -0,0 +1,27 @@
+#include <foot-emulator.h>
+#include "test-common.h"
+
+int main(int argc, char** argv)
+{
+  // CNST
+  // dst - 0, Direct
+  // imm - 0xFFFF
+  {
+    foot::Emulator emu = run_instruction(0x0020FFFF);
+    if (emu.register_at(0) != 0xFFFF) { return 1; }
+  }
+
+  // CNST
+  // dst - 0, Direct
+  // imm - 0xFFFF
+  //
+  // CNST
+  // dst - 0, Indirect
+  // imm = 0x7777
+  {
+    foot::Emulator emu = run_instructions({ 0x0020FFFF, 0x00807777 });
+    if (emu.memory_at(0xFFFF) != 0x7777) { return 1; }
+  }
+
+  return 0;
+}
diff --git a/emulator/tests/test-common.h b/emulator/tests/test-common.h
new file mode 100644
index 0000000..2cdf7a7
--- /dev/null
+++ b/emulator/tests/test-common.h
@@ -0,0 +1,29 @@
+#include <foot-emulator.h>
+
+inline foot::Emulator run_instruction(uint32_t instruction)
+{
+  foot::Emulator emu;
+  emu.memory_at(0) = instruction & 0xFFFF;
+  emu.memory_at(1) = (instruction >> 16) & 0xFFFF;
+
+  emu.run_instruction();
+
+  return emu;
+}
+
+inline foot::Emulator run_instructions(const std::vector<uint32_t>& instructions)
+{
+  foot::Emulator emu;
+  for (int i = 0; i < instructions.size(); i++)
+  {
+    emu.memory_at(i * 2) = instructions[i] & 0xFFFF;
+    emu.memory_at(i * 2 + 1) = (instructions[i] >> 16) & 0xFFFF;
+  }
+
+  for (int i = 0; i < instructions.size(); i++)
+  {
+    emu.run_instruction();
+  }
+
+  return emu;
+}