How should I perform integration testing on a SpringBoot library, that isn't an application - spring

Question

First up, a disclaimer, I'm not entirely happy with the architecture of what I'm about to ask about!
We have a Spring based project that produces a library as a jar. That library includes all the usual controller/service/jpa (repositories) layers you might expect but no boot application to start it all up.
The idea being various projects within our organisation can import the jar and get instant addition of a common (HTTP) API.
Unit tests work ok.
*IT.java tests are another matter.
Run in isolation by the IDE from the test/java/ hierarchy they run ok and pass.
However when running via maven as part of the build they fail.
[ERROR] ControllerIT » IllegalState Unable to find a #SpringBootConfiguration...
We have a Boot configuration in the test hierarchy which the ITs must be using when run via the IDE, but when running the maven build it seems it can't be found to start up the application (understandably as it is in the test package tree).
The boot file we do have is intended to be no more than a test harness to run the lib, to run the ITs.
We have h2 in the Maven test scope, but it isn't wanted in the final library (that is up to the host application to provide a datasource/connection etc).
Requirement:
Start up the API library in an application for testing
Run the tests as part of Maven build
H2 should not end up in final jar
Symptoms when running mvn install
[ERROR] ControllerIT » IllegalState Unable to find a #SpringBootConfiguration...
Presumably need some config somewhere in pom? Already using package.Boot in the Springboot maven plugin config.
Maybe just need to figure out the magic config to point it at the src/test/... Boot.class rather than src/main/...Boot.class
Question(s):
Does spring have a 'correct' way to achieve what we want (I'd go with MicroServices, but not an option because ... reasons)?
How should we go about implementing ITs against a H2 driven SpringBoot application when we don't want to include the bootable class (or H2 lib) in product jar?
Should we be creating a separate Maven module just for the ITs (with a dependency on the library module)?
Abbreviated Maven pom:
<properties>
<version.spring-boot>2.1.13.RELEASE</version.spring-boot>
</properties>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-dependencies</artifactId>
<version>${version.spring-boot}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-rest</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
<exclusion>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
</exclusion>
</exclusions>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-core</artifactId>
<version>2.28.2</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-junit-jupiter</artifactId>
<version>2.28.2</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter</artifactId>
<version>5.4.0</version>
<type>pom</type>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-api</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<scope>test</scope>
</dependency>
<!-- other dependencies excluded for brevity -->
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<version>${version.spring-boot}</version>
<configuration>
<!-- file lives in test hierarchy -->
<mainClass>org.my.packages.test.Boot</mainClass>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>3.0.0-M5</version>
<configuration>
<skip>true</skip><!-- Skipping unit tests while trying to sort ITs -->
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-failsafe-plugin</artifactId>
<version>3.0.0-M5</version>
<configuration>
<failIfNoTests>true</failIfNoTests>
</configuration>
<executions>
<execution>
<goals>
<goal>integration-test</goal>
<goal>verify</goal>
</goals>
</execution>
</execution>
</plugin>
</plugins>
</build>
The Spring Boot config:
#SpringBootApplication()
public class Boot extends SpringBootServletInitializer
{
public static void main(String[] args)
{
SpringApplication.run(Boot.class, args);
}
}
IT configuration:
#SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class ControllerIT
{
#Autowired
private TestRestTemplate restTemplate;
...
}
Number 2 lead me to looking into params of #SpringBootTest.
I ended up with ...
#SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT,
classes = ITConfig.class)
Where ITConfig is:
#SpringBootApplication()
public class ITConfig extends SpringBootServletInitializer
{
public static void main(String[] args)
{
SpringApplication.run(org.lhasalimited.libraries.ITConfig.class, args);
}
}
That appears to be working. Thanks for the hint.

Answer 1

Let me propose one way of solving this issue, there are might be others:
#SpringBootTest annotation is intended to mimic the startup of the full fledged spring boot application.
It scans the packages up to the point where it finds #SpringBootConfiguration annotataion (this annotation is placed on #SpringBootApplication already) and this way it understands that the packages down to the package in which the main class is found should be scanned (to find all the beans).
Besides that, it does many other things that spring boot application does during the start: loading configurations (application.properties/yaml) obeying the conventions of spring boot application, loading auto-configurations (stuff inside spring.factories) and so forth.
Bottom line you'll have a full-fledged spring boot application (usually microservice) loaded inside the test.
So far so good, but you say that you don't really have a spring boot application. So I see three ways:
Introduce an artificial class with #SpringBootConfiguration in the src/test/java/whatever-package-close-to-root folder (note, its in 'test', not in src/main)
Use #SpringBootTest with a parameter of "Configuration". This will mean that SpringBootTest won't use all this scanning up-and-then-down process and instead you'll instruct it to use the concrete context configuration.
Do not use #SpringBootTest annotation at all, and prefer a "usual" #ContextConfiguration - yes, you won't have the power of spring boot but as I've said above you probably won't need it. In addition these tests will be way faster, especially if you'll provide many "#Configuration" classes and will load only "relevant" parts of the library during the tests.
For example, if you test the DAO, there is no point in loading web related stuff.