How to get the value of a variable from java class to JUnit

I am testing the function of my calculator:

//Calculator.java (Pseudo)

parameter 1: int

parameter 2: int

parameter 3: a random number generator 0-3 (0:add, 1:subtract, 2:multiply, 3:divide)

sample: parameter1 (random parameter 3) parameter2

Now, I am having problems in assert because of the parameter 3 (random). Here is my sample code:

//TestCalculator.java
@Test
public void testCalculate() {
    Calculator test = new Calculator();
    int resultCalculate = test.calculate(2, 2);
    actual = //<how can i get the parameter 3 in here to compute the actual result>
    assertEquals(actual, resultCalculate);
}

I can't input a static value in assert, I need to get the value of random first. Help!