Easier DynamoDB local testing

Question

I'm using DynamoDB local for unit testing. It's not bad, but has some drawbacks. Specifically:

• You have to somehow start the server before your tests run
• The server isn't started and stopped before each test so tests become inter-dependent unless you add code to delete all tables, etc. after each test
• All developers need to have it installed

What I want to do is something like put the DynamoDB local jar, and the other jars upon which it depends, in my test/resources directory (I'm writing in Java). Then before each test I'd start it up, running with -inMemory, and after the test I'd stop it. That way anyone pulling down the git repo gets a copy of everything they need to run the tests and each test is independent of the others.

I have found a way to make this work, but it's ugly, so I'm looking for alternatives. The solution I have is to put a .zip file of the DynamoDB local stuff in test/resources, then in the @Before method, I'd extract it to some temporary directory and start a new java process to execute it. That works, but it's ugly and has some drawbacks:

• Everyone needs the java executable on their $PATH
• I have to unpack a zip to the local disk. Using local disk is often dicey for testing, especially with continuous builds and such.
• I have to spawn a process and wait for it to start for each unit test, and then kill that process after each test. Besides being slow, the potential for left-over processes seems ugly.

It seems like there should be an easier way. DynamoDB Local is, after all, just Java code. Can't I somehow ask the JVM to fork itself and look inside the resources to build a classpath? Or, even better, can't I just call the main method of DynamoDB Local from some other thread so this all happens in a single process? Any ideas?

PS: I am aware of Alternator, but it appears to have other drawbacks so I'm inclined to stick with Amazon's supported solution if I can make it work.

Answer 1

In order to use DynamoDBLocal you need to follow these steps.

1. Get Direct DynamoDBLocal Dependency
2. Get Native SQLite4Java dependencies
3. Set sqlite4java.library.path to show native libraries

1. Get Direct DynamoDBLocal Dependency

This one is the easy one. You need this repository as explained in AWS Forums.

<!--Dependency:-->
<dependencies>
    <dependency>
        <groupId>com.amazonaws</groupId>
        <artifactId>DynamoDBLocal</artifactId>
        <version>1.11.0.1</version>
        <scope></scope>
    </dependency>
</dependencies>
<!--Custom repository:-->
<repositories>
    <repository>
        <id>dynamodb-local</id>
        <name>DynamoDB Local Release Repository</name>
        <url>https://s3-us-west-2.amazonaws.com/dynamodb-local/release</url>
    </repository>
</repositories>

2. Get Native SQLite4Java dependencies

If you do not add these dependencies, your tests will fail with 500 internal error.

First, add these dependencies:

<dependency>
    <groupId>com.almworks.sqlite4java</groupId>
    <artifactId>sqlite4java</artifactId>
    <version>1.0.392</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>com.almworks.sqlite4java</groupId>
    <artifactId>sqlite4java-win32-x86</artifactId>
    <version>1.0.392</version>
    <type>dll</type>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>com.almworks.sqlite4java</groupId>
    <artifactId>sqlite4java-win32-x64</artifactId>
    <version>1.0.392</version>
    <type>dll</type>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>com.almworks.sqlite4java</groupId>
    <artifactId>libsqlite4java-osx</artifactId>
    <version>1.0.392</version>
    <type>dylib</type>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>com.almworks.sqlite4java</groupId>
    <artifactId>libsqlite4java-linux-i386</artifactId>
    <version>1.0.392</version>
    <type>so</type>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>com.almworks.sqlite4java</groupId>
    <artifactId>libsqlite4java-linux-amd64</artifactId>
    <version>1.0.392</version>
    <type>so</type>
    <scope>test</scope>
</dependency>

Then, add this plugin to get native dependencies to specific folder:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-dependency-plugin</artifactId>
            <version>2.10</version>
            <executions>
                <execution>
                    <id>copy</id>
                    <phase>test-compile</phase>
                    <goals>
                        <goal>copy-dependencies</goal>
                    </goals>
                    <configuration>
                        <includeScope>test</includeScope>
                        <includeTypes>so,dll,dylib</includeTypes>
                        <outputDirectory>${project.basedir}/native-libs</outputDirectory>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

3. Set sqlite4java.library.path to show native libraries

As last step, you need to set sqlite4java.library.path system property to native-libs directory. It is OK to do that just before creating your local server.

System.setProperty("sqlite4java.library.path", "native-libs");

After these steps you can use DynamoDBLocal as you want. Here is a Junit rule that creates local server for that.

import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClient;
import com.amazonaws.services.dynamodbv2.local.main.ServerRunner;
import com.amazonaws.services.dynamodbv2.local.server.DynamoDBProxyServer;
import org.junit.rules.ExternalResource;

import java.io.IOException;
import java.net.ServerSocket;

/**
 * Creates a local DynamoDB instance for testing.
 */
public class LocalDynamoDBCreationRule extends ExternalResource {

    private DynamoDBProxyServer server;
    private AmazonDynamoDB amazonDynamoDB;

    public LocalDynamoDBCreationRule() {
        // This one should be copied during test-compile time. If project's basedir does not contains a folder
        // named 'native-libs' please try '$ mvn clean install' from command line first
        System.setProperty("sqlite4java.library.path", "native-libs");
    }

    @Override
    protected void before() throws Throwable {

        try {
            final String port = getAvailablePort();
            this.server = ServerRunner.createServerFromCommandLineArgs(new String[]{"-inMemory", "-port", port});
            server.start();
            amazonDynamoDB = new AmazonDynamoDBClient(new BasicAWSCredentials("access", "secret"));
            amazonDynamoDB.setEndpoint("http://localhost:" + port);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    protected void after() {

        if (server == null) {
            return;
        }

        try {
            server.stop();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public AmazonDynamoDB getAmazonDynamoDB() {
        return amazonDynamoDB;
    }

    private String getAvailablePort() {
        try (final ServerSocket serverSocket = new ServerSocket(0)) {
            return String.valueOf(serverSocket.getLocalPort());
        } catch (IOException e) {
            throw new RuntimeException("Available port was not found", e);
        }
    }
}

You can use this rule like this

@RunWith(JUnit4.class)
public class UserDAOImplTest {

    @ClassRule
    public static final LocalDynamoDBCreationRule dynamoDB = new LocalDynamoDBCreationRule();
}