diff --git a/.gitignore b/.gitignore
index 70e53ea..e14759b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,5 @@ venv
 __pycache__
 config.json
 state.json
+.coverage
+test_state.json
diff --git a/README.md b/README.md
index d5cb7f2..535066e 100644
--- a/README.md
+++ b/README.md
@@ -61,7 +61,7 @@ All options are optional (but the companion would do nothing).
 ## Usage
 
 ```
-python3 main.py --help
+python3 companion/main.py --help
 ```
 
 
@@ -69,12 +69,14 @@ python3 main.py --help
 
 Contributions are welcomed! Feel free to update the code and create a pull-request.
 
-Be sure to lint the code before:
+Be sure to lint the code and run tests before:
 
 ```
 docker build -t pre-commit .
 docker run -it -v $(pwd):/mnt/ --rm pre-commit bash
 # cd /mnt/
+# pip install -r requirements.txt
 # pre-commit run --all-files
+# pytest
 # exit
 ```
diff --git a/companion/__init__.py b/companion/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/coingecko.py b/companion/coingecko.py
similarity index 100%
rename from coingecko.py
rename to companion/coingecko.py
diff --git a/config.py b/companion/config.py
similarity index 100%
rename from config.py
rename to companion/config.py
diff --git a/config.schema.json b/companion/config.schema.json
similarity index 100%
rename from config.schema.json
rename to companion/config.schema.json
diff --git a/main.py b/companion/main.py
similarity index 100%
rename from main.py
rename to companion/main.py
diff --git a/pools/__init__.py b/companion/pools/__init__.py
similarity index 100%
rename from pools/__init__.py
rename to companion/pools/__init__.py
diff --git a/pools/ethermine.py b/companion/pools/ethermine.py
similarity index 100%
rename from pools/ethermine.py
rename to companion/pools/ethermine.py
diff --git a/pools/flexpool.py b/companion/pools/flexpool.py
similarity index 100%
rename from pools/flexpool.py
rename to companion/pools/flexpool.py
diff --git a/state.py b/companion/state.py
similarity index 96%
rename from state.py
rename to companion/state.py
index 423fbe8..491d033 100644
--- a/state.py
+++ b/companion/state.py
@@ -20,7 +20,7 @@ class State:
         content = self.read()
         if pool_name not in content:
             content[pool_name] = {}
-        if block_number:
+        if block_number is not None:
             content[pool_name]['block'] = block_number
         if miner_balance is not None:
             content[pool_name]['balance'] = miner_balance
diff --git a/telegram.py b/companion/telegram.py
similarity index 100%
rename from telegram.py
rename to companion/telegram.py
diff --git a/templates/balance.md.j2 b/companion/templates/balance.md.j2
similarity index 100%
rename from templates/balance.md.j2
rename to companion/templates/balance.md.j2
diff --git a/templates/block.md.j2 b/companion/templates/block.md.j2
similarity index 100%
rename from templates/block.md.j2
rename to companion/templates/block.md.j2
diff --git a/templates/payment.md.j2 b/companion/templates/payment.md.j2
similarity index 100%
rename from templates/payment.md.j2
rename to companion/templates/payment.md.j2
diff --git a/utils.py b/companion/utils.py
similarity index 100%
rename from utils.py
rename to companion/utils.py
diff --git a/pytest.ini b/pytest.ini
new file mode 100644
index 0000000..f5c75eb
--- /dev/null
+++ b/pytest.ini
@@ -0,0 +1,2 @@
+[pytest]
+addopts = --cov=companion tests/
diff --git a/requirements.txt b/requirements.txt
index 1ad3230..165da09 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,4 @@
 -r requirements/base.txt
 -r requirements/ethermine.txt
 -r requirements/flexpool.txt
+-r requirements/tests.txt
diff --git a/requirements/tests.txt b/requirements/tests.txt
new file mode 100644
index 0000000..e972258
--- /dev/null
+++ b/requirements/tests.txt
@@ -0,0 +1,2 @@
+pytest==6.2.2
+pytest-cov==2.11.1
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..f1487c8
--- /dev/null
+++ b/tests/__init__.py
@@ -0,0 +1,4 @@
+import os
+import sys
+
+sys.path.append(os.path.join(os.path.dirname(__file__), os.pardir, 'companion'))
diff --git a/tests/test_state.py b/tests/test_state.py
new file mode 100644
index 0000000..f623d5a
--- /dev/null
+++ b/tests/test_state.py
@@ -0,0 +1,100 @@
+import json
+import os
+
+import pytest
+from companion.state import State
+
+
+class TestState:
+    FILENAME = 'test_state.json'
+    POOL_NAME = 'testpool'
+    CONTENT = {
+        'testpool': {
+            'block': 1234,
+            'balance': 1234,
+            'payment': '0x0000000'
+        }
+    }
+
+    @pytest.fixture(scope='function')
+    def state(self):
+        return State(self.FILENAME)
+
+    @pytest.fixture(scope='function')
+    def create_state(self):
+        with open(self.FILENAME, 'w') as fd:
+            json.dump(self.CONTENT, fd, indent=2)
+        yield
+        if os.path.isfile(self.FILENAME):
+            os.unlink(self.FILENAME)
+
+    @pytest.fixture(scope='function')
+    def remove_state(self):
+        yield
+        if os.path.isfile(self.FILENAME):
+            os.unlink(self.FILENAME)
+
+    def test_init(self, state, remove_state):
+        assert os.path.isfile(self.FILENAME)
+        with open(self.FILENAME, 'r') as fd:
+            assert json.load(fd) == {}
+
+    def test_read(self, state, create_state):
+        content = state.read()
+        for pool in self.CONTENT:
+            assert pool in content
+            for key in self.CONTENT[pool]:
+                assert key in content[pool] and content[pool][key] == self.CONTENT[pool][key]
+
+    def test_write(self, state):
+        state.write(pool_name=self.POOL_NAME)
+        content = state.read()
+        assert content[self.POOL_NAME] == {}
+
+    def test_write_block(self, create_state, state):
+        state.write(pool_name=self.POOL_NAME, block_number=5678)
+        content = state.read()
+        assert content[self.POOL_NAME]['block'] == 5678
+
+    def test_write_empty_block(self, create_state, state):
+        state.write(pool_name=self.POOL_NAME, block_number=None)
+        content = state.read()
+        assert content[self.POOL_NAME]['block'] == self.CONTENT[self.POOL_NAME]['block']  # not changed
+
+    def test_write_zero_block(self, create_state, state):
+        state.write(pool_name=self.POOL_NAME, block_number=0)
+        content = state.read()
+        assert content[self.POOL_NAME]['block'] == 0
+
+    def test_write_balance(self, create_state, state):
+        state.write(pool_name=self.POOL_NAME, miner_balance=5678)
+        content = state.read()
+        assert content[self.POOL_NAME]['balance'] == 5678
+
+    def test_write_empty_balance(self, create_state, state):
+        state.write(pool_name=self.POOL_NAME, miner_balance=None)
+        content = state.read()
+        assert content[self.POOL_NAME]['balance'] == self.CONTENT[self.POOL_NAME]['balance']  # not changed
+
+    def test_write_zero_balance(self, create_state, state):
+        state.write(pool_name=self.POOL_NAME, miner_balance=0)
+        content = state.read()
+        assert content[self.POOL_NAME]['balance'] == 0
+
+    def test_write_payment(self, create_state, state):
+        state.write(pool_name=self.POOL_NAME, miner_payment='0x1111111')
+        content = state.read()
+        assert content[self.POOL_NAME]['payment'] == '0x1111111'
+
+    def test_write_empty_payment(self, create_state, state):
+        state.write(pool_name=self.POOL_NAME, miner_payment=None)
+        content = state.read()
+        assert content[self.POOL_NAME]['payment'] == self.CONTENT[self.POOL_NAME]['payment']  # not changed
+
+    def test_get(self, create_state):
+        state = State(filename=self.FILENAME)
+        assert state.get(self.POOL_NAME) == self.CONTENT[self.POOL_NAME]
+
+    def test_get_missing_key(self, create_state):
+        state = State(filename=self.FILENAME)
+        assert state.get('UNKNOWN_POOL') == {}