JUnit 4, testable functions need to be written in a test class?

Question

Java

If I'm testing functions, do they need to be rewritten in the class under test, like in this example?

@RunWith(Parameterized::class)
class MyPresenterTest(var s1:String,
                      var s2:String,
                      var s3:String,
                      var sResult:String) {
companion object{
    @JvmStatic
    @Parameterized.Parameters
    fun testParams() = arrayOf(arrayOf("1","+","1","2"))
}
        fun getResult():String {
            return if (s1.isNotEmpty()&& s2.isNotEmpty()&&s3.isNotEmpty())
            {
                when(s2){
                    "+"->{s1.toInt()+s3.toInt()}
                    "-"->{s1.toInt()-s3.toInt()}
                    "*"->{s1.toInt()*s3.toInt()}
                    "/"->{s1.toInt()/s3.toInt()}
                    else ->{0}
                }.toString()
            }
            else
            {
                return "0"
            }
        }

    @Test
    fun getResultTest() {
        val result=getResult()
        assertEquals(result,sResult)
    }
}

Answer 1

Tests check the code to be executed. There is no point in testing code that won't run.
Tested functions do not need to be written in a test class.