Mockito - 異常處理

Mockito 為模擬物件提供丟擲異常的功能，從而可以測試異常處理。檢視以下程式碼片段。

//add the behavior to throw exception
doThrow(new Runtime Exception("divide operation not implemented"))
   .when(calcService).add(10.0,20.0);

此處我們已將異常子句新增到模擬物件中。MathApplication 使用其 add 方法利用 calcService，並且每當呼叫 calcService.add() 方法時，此模擬物件都會丟擲 RuntimeException。

示例

步驟 1 - 建立名為 CalculatorService 的介面以提供數學函式

檔案：CalculatorService.java

public interface CalculatorService {
   public double add(double input1, double input2);
   public double subtract(double input1, double input2);
   public double multiply(double input1, double input2);
   public double divide(double input1, double input2);
}

步驟 2 - 建立 JAVA 類來表示 MathApplication

檔案：MathApplication.java

public class MathApplication {
   private CalculatorService calcService;

   public void setCalculatorService(CalculatorService calcService){
      this.calcService = calcService;
   }
   
   public double add(double input1, double input2){
      return calcService.add(input1, input2);		
   }
   
   public double subtract(double input1, double input2){
      return calcService.subtract(input1, input2);
   }
   
   public double multiply(double input1, double input2){
      return calcService.multiply(input1, input2);
   }
   
   public double divide(double input1, double input2){
      return calcService.divide(input1, input2);
   }
}

步驟 3 - 測試 MathApplication 類

透過注入 calculatorService 的模擬物件來測試 MathApplication 類。此模擬物件將由 Mockito 建立。

檔案：MathApplicationTester.java

import static org.mockito.Mockito.doThrow;

import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.runners.MockitoJUnitRunner;

// @RunWith attaches a runner with the test class to initialize the test data
@RunWith(MockitoRunner.class)
public class MathApplicationTester {
	
   // @TestSubject annotation is used to identify class 
      which is going to use the mock object
   @TestSubject
   MathApplication mathApplication = new MathApplication();

   //@Mock annotation is used to create the mock object to be injected
   @Mock
   CalculatorService calcService;

   @Test(expected = RuntimeException.class)
   public void testAdd(){
      //add the behavior to throw exception
      doThrow(new RuntimeException("Add operation not implemented"))
         .when(calcService).add(10.0,20.0);

      //test the add functionality
      Assert.assertEquals(mathApplication.add(10.0, 20.0),30.0,0); 
   }
}

步驟 4 - 執行測試用例

在 C:\> Mockito_WORKSPACE 中建立一個名為 TestRunner 的 java 類檔案以執行測試用例。

檔案：TestRunner.java

import org.junit.runner.JUnitCore;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;

public class TestRunner {
   public static void main(String[] args) {
      Result result = JUnitCore.runClasses(MathApplicationTester.class);
      
      for (Failure failure : result.getFailures()) {
         System.out.println(failure.toString());
      }
      
      System.out.println(result.wasSuccessful());
   }
}  	

步驟 5 - 驗證結果

使用 javac 編譯器編譯類，如下所示：

C:\Mockito_WORKSPACE>javac CalculatorService.java MathApplication.
   java MathApplicationTester.java TestRunner.java

現在執行 Test Runner 來檢視結果：

C:\Mockito_WORKSPACE>java TestRunner

驗證輸出。

testAdd(MathApplicationTester): Add operation not implemented
false