Argument Matcher

Example of Argument matcher

We'll make an example of Argument Matchers right now. We're using the anyInt(), anyBoolean function in our test example, although we could use any of the ArgumentMatchers class's methods.

BookServiceTest

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.*;
import org.mockito.junit.jupiter.MockitoExtension;



import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;


import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.mockito.Mockito.*;


@ExtendWith(MockitoExtension.class)
class BookServiceTest {
   @InjectMocks
   private BookService bookService;


   @Mock
   private BookRepository bookRepository;


   @Test
   public void testUpdatePrice() {
       Book book1 = new Book("ISBN5321", "Mockito Test", 600, LocalDate.now());
       Book book2 = new Book("ISBN5321", "Mockito Test", 500, LocalDate.now());
       when(bookRepository.findBookById(any(String.class))).thenReturn(book1);
       bookService.updatePrice("ISBN5321", 500);
       verify(bookRepository).save(book2);
   }


   @Test
   public void testSpecificTypeOfArgumentMatchers() {
       Book book = new Book("ISBN5321", "Mockito Test", 600, LocalDate.now());
       when(bookRepository.findBookByTitleAndPriceAndIsDigital(anyString(), anyInt(), anyBoolean())).thenReturn(book);
       Book actualBook = bookService.getBookByTitleAndPriceAndIsDigital("Mockito Test", 600, true);
       assertEquals("Mockito Test", actualBook.getTitle());
   }


   @Test
   public void testCollectionTypeArgumentMatchers() {
       List<Book> books = new ArrayList<>();
       Book book = new Book("ISBN5321", "Mockito Test", 600, LocalDate.now());
       books.add(book);
       bookService.addBooks(books);
       verify(bookRepository).saveAll(anyList()); // anySet, anyMap, anyCollection
   }


   @Test
   public void testStringTypeArgumentMatchers() {
       Book book = new Book("ISBN5321", "Mockito Test", 600, LocalDate.now());
       when(bookRepository.findBookByTitleAndPriceAndIsDigital(contains("Action"), anyInt(), anyBoolean())).thenReturn(book);
       Book actualBook = bookService.getBookByTitleAndPriceAndIsDigital("JUnit 5 In Action", 600, true);
       assertEquals("Mockito Test", actualBook.getTitle());
   }
}

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FAQs

1. What is an argument matcher?
Ans: Argument matchers are mostly utilised in Mockito to conduct flexible verification and stubbing. To access all of the matcher methods, it extends the ArgumentMatchers class. Equal() is a heritage method that Mockito uses to verify and match parameter values.

2. What is ArgumentCaptor used for?
Ans: ArgumentCaptor lets us investigate an argument supplied to a method by capturing it. This comes in handy when we can't get to the argument outside of the method we're testing.

3. Can the Mockito Matcher methods be used as return values?
Ans: Matcher methods can't be used as return values in Mockito; for example, there's no way to say thenReturn(anyInt()) or thenReturn(any(Foo. class)). Mockito has to know which instance to return in stubbing calls, and it will not select a random return value for you.

4. What are matchers in JUnit?
Ans: Matchers is a third-party component of the JUnit framework. Hamcrest, a framework, was responsible for the addition of matchers. You don't have to download and install Hamcrest because JUnit 4.8. 2 includes it by default.

Read Also -  Difference between argument and parameter

Key Takeaways

In this blog, we have looked into the implementation of argument matchers. There implementation, however, it is recommended to go through the official documentation to learn more and advised to do hands-on practise to get a clear understanding of the article.

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