Custom argument providers in JUnit - Test Execution Trace

Test Overview

This test uses a custom argument provider to supply multiple sets of input data to a parameterized test method. It verifies that the sum of two integers matches the expected result for each data set.

Test Code - JUnit 5

JUnit

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.Arguments;
import org.junit.jupiter.params.provider.ArgumentsProvider;
import org.junit.jupiter.params.provider.ArgumentsSource;
import org.junit.jupiter.api.extension.ExtensionContext;
import java.util.stream.Stream;
import static org.junit.jupiter.api.Assertions.assertEquals;

class CustomArgumentProviderTest {

    static class SumArgumentsProvider implements ArgumentsProvider {
        @Override
        public Stream<Arguments> provideArguments(ExtensionContext context) {
            return Stream.of(
                Arguments.of(1, 2, 3),
                Arguments.of(5, 7, 12),
                Arguments.of(10, 15, 25)
            );
        }
    }

    @ParameterizedTest
    @ArgumentsSource(SumArgumentsProvider.class)
    void testSum(int a, int b, int expectedSum) {
        int actualSum = a + b;
        assertEquals(expectedSum, actualSum, () -> String.format("Sum of %d and %d should be %d", a, b, expectedSum));
    }
}

Execution Trace - 6 Steps

Step	Action	System State	Assertion	Result
1	Test runner starts and identifies the parameterized test method with custom argument provider	JUnit test environment initialized, SumArgumentsProvider ready to supply arguments	-	PASS
2	SumArgumentsProvider.provideArguments() is called to get test data stream	Stream of argument sets [(1,2,3), (5,7,12), (10,15,25)] prepared	-	PASS
3	Test method testSum is invoked with arguments (1, 2, 3)	Test method running with a=1, b=2, expectedSum=3	assertEquals(3, 1+2)	PASS
4	Test method testSum is invoked with arguments (5, 7, 12)	Test method running with a=5, b=7, expectedSum=12	assertEquals(12, 5+7)	PASS
5	Test method testSum is invoked with arguments (10, 15, 25)	Test method running with a=10, b=15, expectedSum=25	assertEquals(25, 10+15)	PASS
6	All parameterized test invocations complete, test run ends	All assertions passed for all argument sets	-	PASS

Failure Scenario

Failing Condition: One of the expected sums does not match the actual sum of the inputs

Execution Trace Quiz - 3 Questions

What does the custom argument provider supply to the test method?

A The test report format

B Multiple sets of input arguments for the test

C The test method's return values

D The test method's annotations

Key Result

Using a custom argument provider helps run the same test logic with different data sets, improving test coverage and reducing code duplication.