diff --git a/btlib/btlib.py b/btlib/btlib.py
index d96ecc3..468fff8 100644
--- a/btlib/btlib.py
+++ b/btlib/btlib.py
@@ -47,11 +47,11 @@ class Strategy(ABC):
 
     @abstractmethod
     def init(self):
-        pass
+        """ Abstract method for initializing resources for the strategy """
 
     @abstractmethod
     def next(self, i: int, record: Dict[Hashable, Any]):
-        pass
+        """ Abstract method defining the core functionality of the strategy """
 
     def __init__(self):
         self.data = pd.DataFrame()
diff --git a/tests/test_backtest.py b/tests/test_backtest.py
index 8b27a3d..d7d79fa 100644
--- a/tests/test_backtest.py
+++ b/tests/test_backtest.py
@@ -88,6 +88,3 @@ def test_backtest_multiple_assets(self):
         pd.testing.assert_series_equal(result.returns, returns)
         self.assertEqual(result.trades, trades)
         self.assertEqual(result.open_positions, open_positions)
-
-if __name__ == '__main__':
-    unittest.main()
\ No newline at end of file
diff --git a/tests/test_position.py b/tests/test_position.py
index 948292e..499e88e 100644
--- a/tests/test_position.py
+++ b/tests/test_position.py
@@ -64,6 +64,3 @@ def test_update_position_with_valid_values(self):
         self.assertAlmostEqual(position.profit_loss, 500.0)
         self.assertAlmostEqual(position.change_pct, 50.0)
         self.assertAlmostEqual(position.current_value, 1500.0)
-
-if __name__ == '__main__':
-    unittest.main()
\ No newline at end of file
diff --git a/tests/test_strategy.py b/tests/test_strategy.py
index 0496c38..dbc6eb3 100644
--- a/tests/test_strategy.py
+++ b/tests/test_strategy.py
@@ -6,9 +6,10 @@
 
 class CustomStrategy(Strategy):
     def init(self):
-        pass
+        """ Implementation for initialization """
+
     def next(self, i, record):
-        pass
+        """ Implementation for the core strategy logic """
 
 class TestStrategy(unittest.TestCase):
 
@@ -42,3 +43,9 @@ def test_open_sets_size_to_cash_divided_by_price_if_size_is_none(self):
         strategy.cash = 100
         self.assertTrue(strategy.open(10, None))
         self.assertEqual(strategy.open_positions[0].position_size, 10)
+
+    # The close() method returns False if price is NaN or less than or equal to zero
+    def test_close_returns_false_if_price_or_size_invalid(self):
+        strategy = CustomStrategy()
+        self.assertFalse(strategy.close(nan))
+        self.assertFalse(strategy.close(0))