Contract testing basics in Testing Fundamentals - Build an Automation Script

Verify API contract between consumer and provider

Preconditions (3)

Step 1: Run the consumer test to generate the contract file

Step 2: Publish the contract file to the contract broker or share with provider

Step 3: Run the provider verification test using the contract file

Step 4: Check that the provider response matches the contract expectations

✅ Expected Result: Provider verification test passes confirming the API contract is fulfilled

Automation Requirements - Pact JVM (Java) or Pact JS (JavaScript)

Assertions Needed:

Verify that provider response status code matches contract

Verify that provider response body matches contract schema and values

Verify that provider headers match contract

Best Practices:

Use explicit contract files shared between consumer and provider

Automate contract verification as part of provider CI pipeline

Use clear and stable request/response examples in contract

Fail tests if provider does not meet contract exactly

Automated Solution

Testing Fundamentals

import au.com.dius.pact.provider.junit5.PactVerificationContext;
import au.com.dius.pact.provider.junit5.PactVerificationInvocationContextProvider;
import au.com.dius.pact.provider.junit5.Provider;
import au.com.dius.pact.provider.junit5.State;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.TestTemplate;
import org.junit.jupiter.api.extension.ExtendWith;

@Provider("UserService")
public class UserServiceProviderTest {

  @BeforeEach
  void before(PactVerificationContext context) {
    context.setTarget(new HttpTestTarget("localhost", 8080));
  }

  @TestTemplate
  @ExtendWith(PactVerificationInvocationContextProvider.class)
  void pactVerificationTestTemplate(PactVerificationContext context) {
    context.verifyInteraction();
  }

  @State("User exists")
  public void userExists() {
    // Setup provider state: ensure user data exists in database
  }

  @State("User does not exist")
  public void userDoesNotExist() {
    // Setup provider state: ensure user data does not exist
  }

}

This code uses the Pact JVM framework to verify the provider API against the contract.

The @Provider annotation names the provider service.

The @BeforeEach method sets the target URL where the provider API runs.

The @TestTemplate method runs all interactions defined in the contract file.

The @State methods set up provider data states required by the contract scenarios.

This structure ensures the provider API responses match the consumer expectations defined in the contract.

Common Mistakes - 3 Pitfalls

Not setting up provider states before verification

Running provider verification without the correct contract file

Ignoring header verification in contract tests

Bonus Challenge

Now add data-driven contract tests for multiple user IDs with different expected responses

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