Show List
Tutorials > Mockito > Using Mockito to test exceptions and error conditions

Using Mockito to test exceptions and error conditions

When writing unit tests, it's important to test not only the normal behavior of your code, but also the exceptional cases, such as when an exception is thrown or an error condition occurs. Mockito makes it easy to test exceptions and error conditions in your code by providing a set of methods that allow you to simulate these conditions and verify that your code handles them correctly.

Here's an example of how to use Mockito to test exceptions and error conditions:

Let's say you have a class called "StringUtils" with a method called "reverse" that reverses a string. However, if the string is null or empty, the method should throw an IllegalArgumentException.

typescript
Copy code
public class StringUtils {
  public static String reverse(String str) {
    if (str == null || str.isEmpty()) {
      throw new IllegalArgumentException("String cannot be null or empty");
    }

    StringBuilder sb = new StringBuilder(str);
    return sb.reverse().toString();
  }
}

To test this method using Mockito, you would need to do the following:

  • Create a test method that uses the JUnit @Test annotation.
typescript
Copy code
@Test
public void testReverse() {
  // test code goes here
}
  • Call the StringUtils.reverse() method with a null string and verify that it throws the expected exception.
scss
Copy code
try {
  StringUtils.reverse(null);
  fail("Expected an IllegalArgumentException to be thrown");
} catch (IllegalArgumentException e) {
  assertEquals("String cannot be null or empty", e.getMessage());
}
  • Call the StringUtils.reverse() method with an empty string and verify that it throws the expected exception.
scss
Copy code
try {
  StringUtils.reverse("");
  fail("Expected an IllegalArgumentException to be thrown");
} catch (IllegalArgumentException e) {
  assertEquals("String cannot be null or empty", e.getMessage());
}
  • Call the StringUtils.reverse() method with a non-empty string and verify that it returns the expected result.
sql
Copy code
String result = StringUtils.reverse("hello");
assertEquals("olleh", result);

Here's the full example:

typescript
Copy code
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.fail;
import org.junit.Test;

public class StringUtilsTest {

  @Test
  public void testReverse() {
    try {
      StringUtils.reverse(null);
      fail("Expected an IllegalArgumentException to be thrown");
    } catch (IllegalArgumentException e) {
      assertEquals("String cannot be null or empty", e.getMessage());
    }

    try {
      StringUtils.reverse("");
      fail("Expected an IllegalArgumentException to be thrown");
    } catch (IllegalArgumentException e) {
      assertEquals("String cannot be null or empty", e.getMessage());
    }

    String result = StringUtils.reverse("hello");
    assertEquals("olleh", result);
  }
}

This example demonstrates how to use Mockito to test exceptions and error conditions in your code. By using the try-catch block and the fail() method to verify that the expected exceptions are thrown, you can ensure that your code handles these exceptional cases correctly.



Next: Verifying method calls with Mockito

    Leave a Comment

  • captcha text