Replay in JUnit

The Java flow mirrors Replay in Jest. Same case file, same control API, same findInCase + mockOutbound pattern — just JUnit 5 and java.net.http.HttpClient instead of Jest and fetch.

1. Add the dependency

<dependency>
  <groupId>dev.softprobe</groupId>
  <artifactId>softprobe-java</artifactId>
  <version>0.5.0</version>
  <scope>test</scope>
</dependency>

JUnit 5 is assumed (junit-jupiter-engine etc.).

2. The minimum working test

// src/test/java/com/example/CheckoutReplayTest.java
package com.example;

import dev.softprobe.Softprobe;
import dev.softprobe.SoftprobeSession;
import dev.softprobe.CapturedHit;
import org.junit.jupiter.api.*;

import java.net.URI;
import java.net.http.*;
import java.nio.file.Paths;

import static org.junit.jupiter.api.Assertions.*;

@TestInstance(TestInstance.Lifecycle.PER_CLASS)
class CheckoutReplayTest {

    private final Softprobe softprobe = new Softprobe(
        System.getenv().getOrDefault("SOFTPROBE_RUNTIME_URL", "http://127.0.0.1:8080")
    );
    private final String appUrl =
        System.getenv().getOrDefault("APP_URL", "http://127.0.0.1:8082");

    private SoftprobeSession session;

    @BeforeAll
    void setUp() throws Exception {
        session = softprobe.startSession("replay");
        session.loadCaseFromFile(
            Paths.get("cases", "checkout-happy-path.case.json").toString()
        );

        CapturedHit hit = session.findInCase(
            CaseSpanPredicate.builder()
                .direction("outbound")
                .method("POST")
                .hostSuffix("stripe.com")
                .pathPrefix("/v1/payment_intents")
                .build()
        );

        session.mockOutbound(
            MockRuleSpec.builder()
                .direction("outbound")
                .method("POST")
                .hostSuffix("stripe.com")
                .pathPrefix("/v1/payment_intents")
                .response(hit.getResponse())
                .build()
        );
    }

    @AfterAll
    void tearDown() throws Exception {
        session.close();
    }

    @Test
    void chargesTheCapturedCard() throws Exception {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create(appUrl + "/checkout"))
            .header("content-type", "application/json")
            .header("x-softprobe-session-id", session.getId())
            .POST(HttpRequest.BodyPublishers.ofString("{\"amount\":1000,\"currency\":\"usd\"}"))
            .build();

        HttpResponse<String> response = client.send(request,
            HttpResponse.BodyHandlers.ofString());

        assertEquals(200, response.statusCode());
        assertTrue(response.body().contains("\"status\":\"paid\""));
    }
}

3. Run it

mvn test

Expected:

[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] BUILD SUCCESS

API parity

JavaScript	Java
new Softprobe({ baseUrl })	new Softprobe(baseUrl)
softprobe.startSession({ mode: 'replay' })	softprobe.startSession("replay")
session.loadCaseFromFile(path)	session.loadCaseFromFile(path)
session.findInCase({ direction, … })	session.findInCase(CaseSpanPredicate.builder()...build())
session.mockOutbound({ …, response })	session.mockOutbound(MockRuleSpec.builder()...build())
session.clearRules()	session.clearRules()
session.setPolicy({ externalHttp: 'strict' })	session.setPolicy(Policy.strict())
session.close()	session.close()

Builder-pattern DTOs (CaseSpanPredicate.builder(), MockRuleSpec.builder()) make the fluent Java API read similarly to the JavaScript object literals.

Using the JUnit extension

Boilerplate (create/close session, inject into the test class) can be delegated to a JUnit extension:

@ExtendWith(SoftprobeExtension.class)
class CheckoutReplayTest {
    @SoftprobeSession(mode = "replay", casePath = "cases/checkout-happy-path.case.json")
    SoftprobeSession session;

    @Test
    void chargesTheCapturedCard() throws Exception {
        var hit = session.findInCase(CaseSpanPredicate.builder()
            .direction("outbound").hostSuffix("stripe.com").build());
        session.mockOutbound(MockRuleSpec.builder()
            .hostSuffix("stripe.com").response(hit.getResponse()).build());

        // ... your HTTP call and assertions
    }
}

Parallel tests

Configure JUnit 5 parallel execution in junit-platform.properties:

junit.jupiter.execution.parallel.enabled = true
junit.jupiter.execution.parallel.mode.default = concurrent
junit.jupiter.execution.parallel.config.fixed.parallelism = 8

Each test class should create its own session; the runtime handles many in parallel.

Next

• Java SDK reference — complete API.
• Run a suite at scale — for hundreds of cases.
• CI integration — running mvn test in CI with the Softprobe stack.