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Migrate to AssertJ from JUnit Asserts

In this tutorial, we'll use OpenRewrite to perform an automated migration from JUnit Asserts to AssertJ. AssertJ is a Java library that provides a rich set of assertions and truly helpful error messages, improves test code readability, and is designed to be super easy to use within your favorite IDE.

Source available recipe module

This guide uses org.openrewrite.recipe:rewrite-testing-frameworks, a Moderne source-available recipe module. Compiled binaries are only available to Moderne customers, hosted at the Code Genome Project. For non-commercial use you can compile and publish the recipe module locally to use the recipes.

Example Configuration​

The migrate to AssertJ recipe can be applied by adding OpenRewrite's plugin to your project and including a dependency on rewrite-testing-frameworks:

This recipe has no required configuration options. It can be activated by adding a dependency on `org.openrewrite.recipe:rewrite-testing-frameworks` in your build file or by running a shell command (in which case no build changes are needed):

OpenRewrite artifacts, including the Maven and Gradle plugins themselves, are distributed through the Code Genome Project repository (https://artifacts.codegenomeproject.org/maven), which requires authentication. Sign in to the Code Genome Project to create a download token; your build authenticates with the email or username you signed in with, plus that token as the password. See the quickstart guide for details.

  1. Put your Code Genome Project credentials in ~/.gradle/gradle.properties, so that they are not committed alongside your build:
    ~/.gradle/gradle.properties
    codeGenomeUsername=you@example.com
    codeGenomeToken=your-download-token
  2. Add the Code Genome Project repository to your settings.gradle file, so that the plugin itself can be resolved:
    settings.gradle
    pluginManagement {
        repositories {
            maven {
                url = "https://artifacts.codegenomeproject.org/maven"
                credentials {
                    username = providers.gradleProperty("codeGenomeUsername").get()
                    password = providers.gradleProperty("codeGenomeToken").get()
                }
            }
            // Keep the portal for any other plugins your build applies
            gradlePluginPortal()
        }
    }
  3. Add the following to your build.gradle file:
    build.gradle
    plugins {
        id("org.openrewrite.rewrite") version("latest.release")
    }

    rewrite {
        activeRecipe("org.openrewrite.java.testing.assertj.JUnitToAssertj")
    }

    repositories {
        mavenCentral()
        maven {
            url = "https://artifacts.codegenomeproject.org/maven"
            credentials {
                username = providers.gradleProperty("codeGenomeUsername").get()
                password = providers.gradleProperty("codeGenomeToken").get()
            }
        }
    }

    dependencies {
        rewrite("org.openrewrite.recipe:rewrite-testing-frameworks:3.45.0")
    }
  4. Run gradle rewriteRun to run the recipe.

At this point, you're ready to execute the migration by running mvn rewrite:run or gradlew rewriteRun. After running the migration you can inspect the results with git diff (or equivalent), manually fix anything that wasn't able to be migrated automatically, and commit the results.

Before and After​

For the full list of changes, this recipe will make, see its reference page.

package org.openrewrite.example;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.junit.jupiter.api.Assertions.fail;
import static org.junit.jupiter.api.Assertions.assertThrows;

public class ExampleJunitTestClass {

    @Test
    void someTest() {
        try {
            QueryRegistry queryRegistry = new QueryRegistry.Builder().build();
            fail();
        } catch (IllegalArgumentException ignored) {
        }

        // ...

        assertEquals(1, currentSubs.size());
        assertEquals("myPrefix_subId", currentSubs.get(0).getSubscriptionId());
        assertTrue(allSubscriptions.containsKey("myApp"));
    }

    @Test
    void shouldFailToInitializeWithMissingTable() {
        when(catalog.loadTable(any())).thenThrow(new RuntimeException());
        IcebergWriterStage stage = new IcebergWriterStage();
        assertThrows(RuntimeException.class, () -> stage.init(context));
    }
}

See how this recipe works across multiple open-source repositories​

Run this recipe on OSS repos at scale with the Moderne SaaS.

The community edition of the Moderne platform enables you to easily run recipes across thousands of open-source repositories.

Please contact Moderne for more information about safely running the recipes on your own codebase in a private SaaS.