How to test data source injected with @Resource

I want to create some integration tests for the following class:

public class MyDao {
    @Inject
    @Postgres
    private DataSource dataSource;

    getSomething() {
        //do something with dataSource
    }
}

I have the qualifier:

@Qualifier
@Target({ TYPE, METHOD, FIELD, PARAMETER })
@Retention(RUNTIME)
public @interface Postgres {
}

And also I have a producer:

public class PostgresDataSourceProducer {

    @Resource(mappedName = "java:jboss/PostgresDS")
    private DataSource ds;

    @Produces
    @Postgres
    DataSource postgresDataSouce() {
        return ds;
    }
}

I'm using wildfly 14. Data source was defined in the standalone.xml:

<subsystem xmlns="urn:jboss:domain:datasources:5.0">
        <datasources>
            <datasource jta="false" jndi-name="java:jboss/PostgresDS" pool-name="postgres" enabled="true" use-ccm="false">
                <connection-url>jdbc:postgresql://${production.postgres.url}</connection-url>
                <driver-class>org.postgresql.Driver</driver-class>
                <driver>postgresql-8.0-310.jdbc3.jar</driver>
                <security>
                    <user-name>${db.username}</user-name>
                    <password>${db.userpass}</password>
                </security>
                <validation>
                    <validate-on-match>false</validate-on-match>
                    <background-validation>false</background-validation>
                </validation>
                <statement>
                    <share-prepared-statements>false</share-prepared-statements>
                </statement>
            </datasource>
        </datasources>
</subsystem>

To create integration tests, I will need to change the datasource to point to my test database. How to do that?

Because it'a a legacy code, I'm reserved to switch from @Resource to @PersistenceContext.

There are many ways to do this, but first, define your test data-source in the subsystem (let's map it with java:jboss/H2 for the sake of the examples below).

Via the CDI @Alternative

Create another producer class for the test data-source and marked it as an alternative.

Example:

public class PostgresDataSourceProducer {

    @Resource(mappedName = "java:jboss/PostgresDS")
    private DataSource primary;

}

@Alternative
public class H2DataSourceProducer {

    @Resource(mappedName = "java:jboss/H2")
    private DataSource test;

}

In the test resource directory, add a new CDI descriptor file specifically for tests. You may want to copy the configs from the main descriptor file to retain behaviors or avoid runtime errors.

Example:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://xmlns.jcp.org/xml/ns/javaee"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/beans_1_1.xsd"
       version="1.1" bean-discovery-mode="all">
    <alternatives>
         <class>path.to.your.datasource.H2DataSourceProducer</class>
    </alternatives>
</beans>

And lastly, when creating your test artifacts via Shrinkwrap, replace the CDI descriptor files for the affected modules with the one above.

Example:

final var services = ...;
services.addAsManifestResource("META-INF/beans.xml", "beans.xml");

Via the JPA Persistence-unit config

You may also just scrape the data-source producer and let JPA get the correct data-source at runtime via the persistence-unit config.

Add a new persistence.xml file in the test resource directory. Retain everything from the main persistence config except for the data-source property.

Example:

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_2.xsd"
             version="2.2">
    <persistence-unit name="primary">
        
        <!--<jta-data-source>java:jboss/PostgresDS</jta-data-source>-->
        <jta-data-source>java:jboss/H2</jta-data-source>
        ...
    </persistence-unit>
</persistence>

And lastly, when creating your test artifacts via Shrinkwrap, replace the main persistence config file with the one above.