Added more unit tests

test.py

@@ -2,8 +2,11 @@
 
 # import pytest
 
-from calculator import add
+from calculator import add, multiply, subtract
 
 def test_add():
     assert add(2, 2) == 4
-
+def test_subtract():
+    assert subtract(2, 2) == 0
+def test_multiply():
+    assert multiply(2, 3) == 6