Summary - Mockito

Combine Mock, when and verify to write a service test.

Summary - Mockito

In this group you saw the core tools of Mockito: mock() for fake objects, @Mock and @InjectMocks for field-based setup, when().thenReturn() for behavior, verify() for interaction checks and ArgumentMatchers for flexible matching.

Now you will combine these into a mini task: building stub and verify logic by hand for an OrderService. This summary shows how mocks really work.

Exercise Build a stub for OrderService

Define an OrderService class with a double priceFor(String sku) method that looks up a Map<String, Double> table and returns the price; for an unknown sku it returns 0.0. In an OrderDemo class write main; add put("A1", 9.99) and put("B2", 4.50) to the table; print the result of priceFor("A1").

Show example solution

import java.util.*;

class OrderService {
    Map<String, Double> table = new HashMap<>();
    double priceFor(String sku) {
        return table.getOrDefault(sku, 0.0);
    }
}

class OrderDemo {
    public static void main(String[] args) {
        OrderService s = new OrderService();
        s.table.put("A1", 9.99);
        s.table.put("B2", 4.50);
        System.out.println(s.priceFor("A1"));
    }
}

Exercise Add an interaction counter

Define a new CallTracker class with an int count field and a void record(String sku) method that increments count each call. In a TrackerDemo class write main; call record twice and print count.

Show example solution

class CallTracker {
    int count = 0;
    void record(String sku) {
        count++;
    }
}

class TrackerDemo {
    public static void main(String[] args) {
        CallTracker t = new CallTracker();
        t.record("A1");
        t.record("B2");
        System.out.println(t.count);
    }
}

Test yourself

What is used to define a return value for a mocked method?
- verify
- @Mock
- any()
- when(...).thenReturn(...)
Show answer

when(...).thenReturn(...) — when(...).thenReturn(...) defines the return value.
Match the Mockito summary

mock()

Builds a fake object
@Mock

Marks a field as mock
when

Defines behavior
verify

Checks calls

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