Configure specific in memory database for testing purpose in Spring

Simplest solution:

1) in src/main/resources have application.properties (production config):

spring.datasource.url=jdbc:mysql://localhost:3306/somedb
spring.datasource.username=root
spring.datasource.password=password
spring.datasource.driverClassName=com.mysql.jdbc.Driver
spring.jpa.database-platform = org.hibernate.dialect.MySQL5Dialect

and application-test.properties with HSQL config like:

spring.jpa.hibernate.ddl-auto = create-drop
spring.jpa.database = HSQL
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.HSQLDialect
spring.datasource.driverClassName = org.hsqldb.jdbcDriver
spring.datasource.url= jdbc:hsqldb:mem:scratchdb
spring.datasource.username = sa
spring.datasource.password =

2) Add HSQL dependency in pom.xml if you don't have it already.

3) Annotate your test class with @ActiveProfiles("test").

Worked like charm in my case.

Another approach is to add the annotation @AutoConfigureTestDatabase to you test class. My tests usually look like this:

@RunWith(SpringRunner.class)
@DataJpaTest
@AutoConfigureTestDatabase(connection = EmbeddedDatabaseConnection.H2)
public class MyRepositoryTest {

    @Autowired
    MyRepository repository;

    @Test
    public void test() throws Exception {
        // Tests...
    }
}

Note that the embedded database dependency needs to be added in the pom.xml file. For embedded database this annotation is not necessary it will work even if only the dependency is added in pom file.

Spring profiles can be used for this. This would be a specific way:

Have environment specific properties files:

application.properties:

spring.profiles.active: dev

application-dev.properties

spring.jpa.database: MYSQL
spring.jpa.hibernate.ddl-auto: update

spring.datasource.url: jdbc:mysql://localhost:3306/dbname
spring.datasource.username: username
spring.datasource.password: password

application-test.properties

spring.jpa.database: HSQL

Have both MySQL and H2 drivers in pom.xml, like this:

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <scope>runtime</scope>
</dependency>

<dependency>
    <groupId>org.hsqldb</groupId>
    <artifactId>hsqldb</artifactId>
    <scope>test</scope>
</dependency>

Last but not the least, annotate Test classes with @ActiveProfiles("test").

With @SpringBootTest magic, you just need to do following two changes.

1. Add 'h2' test dependency in pom.xml

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <scope>test</scope>
</dependency>

2. Use @AutoConfigureTestDatabase

@RunWith(SpringRunner.class)
@SpringBootTest(classes = MySpringBootApplication.class)
@AutoConfigureTestDatabase
public class SpringBootTest{

    @Autowired
    private RequestRepository requestRepository;
}

Now all the spring jpa bean/repositories used in test will use h2 as backing database.

2019-04-26 13:13:34.198 INFO 28627 --- [ main] beddedDataSourceBeanFactoryPostProcessor : Replacing 'dataSource' DataSource bean with embedded version

2019-04-26 13:13:34.199 INFO 28627 --- [ main] o.s.b.f.s.DefaultListableBeanFactory : Overriding bean definition for bean 'dataSource'

2019-04-26 13:13:36.194 INFO 28627 --- [ main] o.s.j.d.e.EmbeddedDatabaseFactory : Starting embedded database: url='jdbc:h2:mem:2784768e-f053-4bb3-ab88-edda34956893;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=false', username='sa'

Note: I still have 'spring-jpa' properties defined in 'application.properties' and I don't use any profiles. @AutoConfigureTestDatabase will override existing jpa configurations with test defaults AutoConfigureTestDatabase.Replace.