Can I specify in gradle that I only want to use a certain plugin for tests? - spring-boot

Question

I have a project and for testing purposes only I want to standup a quick websocket server. Spring Boot seems like the simplest way to do that, but I don't want to include the plugin in my implementation, only for tests. I can't seem to find documentation on something like this, but in general I've found the answer to the question "can gradle do this" is usually yes.
So how would I go about specifying to only use the 'org.springframework.boot' plugin for test builds?
I've tried placing the plugins {} block inside a test {} block but that doesn't work.

Answer 1

I'm pretty sure you may just apply the org.springframework.boot plugin in the regular way and it won't effect your build artifacts.
However, it is possible to apply plugins dynamically, if you are afraid that they might have undesired side-effects on build artifacts. The old plugin mechanism actually worked this way by default and separated the resolution of plugins from their application to the Project instance:
// This part resolves the plugin
buildscript {
repositories {
maven {
url 'https://plugins.gradle.org/m2/'
}
}
dependencies {
classpath 'org.springframework.boot:spring-boot-gradle-plugin:2.3.2.RELEASE'
}
}
// This part applies the plugin
apply plugin: 'org.springframework.boot'
This way it was possible to apply a plugin based on a condition:
if (testMode) {
apply plugin: 'org.springframework.boot'
}
Using the new plugins block to apply plugins, this is not possible directly, as the plugins block is a special block that does not allow custom code:
// This is not allowed!
plugins {
if (testMode) {
id 'org.springframework.boot' version '2.3.2.RELEASE'
}
}
The solution is to tell the plugins block to resolve a plugin without applying it automatically. This can then be done dynamically using apply plugin::
plugins {
id 'org.springframework.boot' version '2.3.2.RELEASE' apply false
}
if (testMode) {
apply plugin: 'org.springframework.boot'
}

Answer 2

You don't have to use org.springframework.boot plugin: just use io.spring.dependency-management plugin. This way, you will be able to declare spring-* related dependencies in your testImplementation configuration, without any impact on the implementation configuration.
plugins {
id 'io.spring.dependency-management' version '1.0.8.RELEASE'
id 'java'
}
dependencies {
testImplementation 'org.springframework.boot:spring-boot-starter'
testImplementation 'org.springframework.boot:spring-boot-starter-websocket'
testImplementation('org.springframework.boot:spring-boot-starter-test') {
exclude group: 'org.junit.vintage', module: 'junit-vintage-engine'
}
}
dependencyManagement {
imports {
mavenBom "org.springframework.boot:spring-boot-dependencies:2.2.0.RELEASE"
}
}
Then in your test sources, you will be able to declare SpringBoot application and other websocket-related stuff (controllers)
EDIT what org.springframework.boot is actually doing, is to change the packaging of the main jar artifact by declaring the bootJar task, see Springboot plugin reference. In your case you don't need this, as far as I understand, if you just want to run some Spring application in test sourceset.