Using Jbehave. Starting simple...
Scenario: 1 add
Given a variable x with value 2 When I add x with 4 Then x should equal 6
Scenario: 2 multiply
Given a variable x with value 8 When I multiply x by 8 Then x should equal 64
Scenario: 3 multiply-fail
Given a variable x with value 3 When I multiply x by 3 Then x should equal 10
Scenario: 4 power
Given a variable x with value 2 When I power x to 3 Then x should equal 8