increment and decrement function added.

engine/eval/functions.py

@@ -64,3 +64,27 @@ def __repr__(self) -> str:
     def calculate(self, value: int) -> int:
         """Calculate the integer square root of given value."""
         return int(math.sqrt(value))
+
+
+class Increment(Function):
+    """Calculate +1 of variable value."""
+
+    def __repr__(self) -> str:
+        """String representation of the increment function."""
+        return "Increment(%s)" % super().__repr__()
+
+    def calculate(self, value: int) -> int:
+        """Calculate the increment of given value."""
+        return value + 1
+
+
+class Decrement(Function):
+    """Calculate -1 of variable value."""
+
+    def __repr__(self) -> str:
+        """String representation of the decrement function."""
+        return "Decrement(%s)" % super().__repr__()
+
+    def calculate(self, value: int) -> int:
+        """Calculate the decrement of given value."""
+        return value - 1

tests/test_engine_eval_functions.py

@@ -7,7 +7,7 @@
 from hamcrest import assert_that, equal_to, calling, raises
 
 from engine.eval.variable import Variable
-from engine.eval.functions import Square, SumOfDigits, SquareRoot
+from engine.eval.functions import Square, SumOfDigits, SquareRoot, Increment, Decrement
 
 
 class BadVariable(Variable):
@@ -46,3 +46,15 @@ def test_integer_square_root(self):
         fun = SquareRoot(Variable(1025))
         assert_that(fun.get(), equal_to(32))
         assert_that(str(fun), "SquareRoot(Variable(1025))")
+
+    def test_increment(self):
+        """Testing increment function."""
+        fun = Increment(Variable(10))
+        assert_that(fun.get(), equal_to(11))
+        assert_that(str(fun), "Increment(Variable(10))")
+
+    def test_decrement(self):
+        """Testing decrement function."""
+        fun = Decrement(Variable(10))
+        assert_that(fun.get(), equal_to(9))
+        assert_that(str(fun), "Decrement(Variable(10))")