EMICalculatorTestFinal.dart

//Domain Entity responsible for calculating EMI for given params.
class EMICalculator {

  final double amount, rate, time;
  EMICalculator(this.amount, this.rate, this.time){
    if(amount<0)
      throw ArgumentError("Amount cannot be less than zero");
    if(rate<0)
      throw ArgumentError("Rate cannot be less than zero");
    if(time<0)
      throw ArgumentError("Time cannot be less than zero");
  }

  //EMI = amount× rate × (1 + rate)time/((1 + rate)time-1).
  double calculateEMI()
  {
    return amount*rate*(1 + rate)*time/((1+rate)*time-1);
  }
}

//TEST CASES
  test("Amount cannot be null",()
  {
    EMICalculator emiCalculator=EMICalculator(1,2,3);
    //Performing assertion
    expect(emiCalculator.amount,isNot(null), reason:"Amount cannot be null");
  });

  test("Rate cannot be null",()
  {
    EMICalculator emiCalculator=EMICalculator(1,2,3);
    //Performing assertion
    expect(emiCalculator.rate,isNot(null),reason:"Rate cannot be null");
  });

  test("Rate cannot be null",()
  {
    EMICalculator emiCalculator=EMICalculator(1,2,3);
    //Performing assertion
    expect(emiCalculator.time,isNot(null),reason:"Time cannot be null");
  });

  test("EMI cannot be negative",()
  {
    EMICalculator emiCalculator=EMICalculator(1,2,3);
    //Performing assertion
    expect(emiCalculator.calculateEMI(),greaterThan(0),reason:"EMI cannot be negative");
  });


  test("Amount cannot be negative",()
  {
    EMICalculator emiCalculator=EMICalculator(1000,12,3);
    //Performing assertion
    expect(emiCalculator.rate,greaterThan(-1),reason:"Amount cannot be negative");
  });

  test("Rate cannot be negative",()
  {
    EMICalculator emiCalculator=EMICalculator(1,2,3);
    //Performing assertion
    expect(emiCalculator.rate,greaterThan(-1),reason:"Rate cannot be negative");
  });

  test("Time cannot be negative",()
  {
    EMICalculator emiCalculator=EMICalculator(1,2,3);
    //Performing assertion
    expect(emiCalculator.rate,greaterThan(-1),reason:"Rate cannot be negative");
  });

  test("EMI must 150391.64490861617 for amount =10,000 , rate = 15, time =24 months",(){

    EMICalculator emiCalculator=EMICalculator(10000,15,24);
    //We are asserting factual data with our implemented behavior
    expect(150391.64490861617,equals( emiCalculator.calculateEMI()),reason: "Emi calculation invalid");

  });