Move test code depending on Spring to separate module

It is difficult to depend on Spring 6 in test code in our published modules because we maintain a Java 8 baseline while Spring 6 requires Java 17. Moving this code to a separate module avoids that issue. There is still one usage of Spring in our normal test code for ModifiedClassPathClassLoader.

dependencies.gradle

@@ -66,8 +66,6 @@ def VERSIONS = [
         libs.mongoSync,
         libs.postgre,
         libs.slf4jApi,
-        libs.spring.context,
-        libs.spring.core,
         libs.testcontainers.junitJupiter,
         libs.testcontainers.kafka,
         libs.testcontainers.postgresql,

docs/build.gradle

@@ -16,10 +16,29 @@ apply plugin: 'org.antora'
 
 description = 'Micrometer Docs'
 
+// Spring 6 requires Java 17+
+// skip this module when building with jdk <17
+if (!javaLanguageVersion.canCompileOrRun(17)) {
+    project.tasks.configureEach { task -> task.enabled = false }
+}
+
 repositories {
     mavenCentral()
 }
 
+java {
+    toolchain {
+        languageVersion = javaLanguageVersion
+    }
+}
+
+compileTestJava {
+    // need to override the config applied in the root build.gradle to all subprojects
+    // TODO can we not do this with Gradle's toolchains instead?
+    sourceCompatibility = javaLanguageVersion
+    targetCompatibility = javaLanguageVersion
+}
+
 dependencies {
     implementation project(':micrometer-core')
     implementation 'io.micrometer:context-propagation'
@@ -31,7 +50,7 @@ dependencies {
     testImplementation libs.aspectjweaver
     testImplementation libs.junitJupiter
     testImplementation 'org.assertj:assertj-core'
-    testImplementation 'org.springframework:spring-context'
+    testImplementation(libs.spring6.context)
     testImplementation 'io.projectreactor:reactor-core'
     testImplementation 'io.projectreactor:reactor-test'
     testImplementation 'io.netty:netty-transport'

gradle/libs.versions.toml

@@ -75,7 +75,8 @@ rest-assured = "5.5.0"
 signalfx = "1.0.46"
 slf4j = "1.7.36"
 spectator-atlas = "1.7.21"
-spring = "5.3.36"
+spring5 = "5.3.39"
+spring6 = "6.1.13"
 spring-javaformat = "0.0.43"
 testcontainers = "1.20.2"
 tomcat = "8.5.100"
@@ -134,6 +135,8 @@ httpcomponents-client = { module = "org.apache.httpcomponents:httpclient", versi
 httpcomponents-client5 = { module = "org.apache.httpcomponents.client5:httpclient5", version.ref = "httpcomponents-client5" }
 hystrix = { module = "com.netflix.hystrix:hystrix-core", version.ref = "hystrix" }
 jacksonDatabind = { module = "com.fasterxml.jackson.core:jackson-databind", version.ref = "jackson-databind" }
+jakarta-annotationAPi = { module = "jakarta.annotation:jakarta.annotation-api", version = "3.0.0" }
+jakarta-injectApi = { module = "jakarta.inject:jakarta.inject-api", version = "2.0.1" }
 jakarta-jmsApi = { module = "jakarta.jms:jakarta.jms-api", version = "3.0.0" }
 jakarta-servletApi = { module = "jakarta.servlet:jakarta.servlet-api", version = "5.0.0" }
 javalin = { module = "io.javalin:javalin", version = "5.6.5" }
@@ -202,10 +205,11 @@ signalfx = { module = "com.signalfx.public:signalfx-java", version.ref = "signal
 slf4jApi = { module = "org.slf4j:slf4j-api", version.ref = "slf4j" }
 slfj4Simple = { module = "org.slf4j:slf4j-simple", version.ref = "slf4j" }
 spectatorAtlas = { module = "com.netflix.spectator:spectator-reg-atlas", version.ref = "spectator-atlas" }
-spring-context = { module = "org.springframework:spring-context", version.ref = "spring" }
-spring-core = { module = "org.springframework:spring-core", version.ref = "spring" }
+spring5-core = { module = "org.springframework:spring-core", version.ref = "spring5" }
 spring-cloud = { module = "org.springframework.cloud:spring-cloud-dependencies", version = "2021.0.9" }
 spring-javaformatCheckstyle = { module = "io.spring.javaformat:spring-javaformat-checkstyle", version.ref = "spring-javaformat" }
+spring6-aop = { module = "org.springframework:spring-aop", version.ref = "spring6" }
+spring6-context = { module = "org.springframework:spring-context", version.ref = "spring6" }
 systemStubsJupiter = { module = "uk.org.webcompere:system-stubs-jupiter", version = "2.1.7" }
 testcontainers-junitJupiter = { module = "org.testcontainers:junit-jupiter", version.ref = "testcontainers" }
 testcontainers-kafka = { module = "org.testcontainers:kafka", version.ref = "testcontainers" }

micrometer-core/build.gradle

@@ -143,13 +143,15 @@ dependencies {
 
     // dependency injection tests
     testImplementation 'javax.inject:javax.inject'
-    testImplementation 'org.springframework:spring-context'
     testImplementation 'com.google.inject:guice'
 
     // Uncomment these if you are interested in testing injection with dagger in MeterRegistryInjectionTest
     // testImplementation 'com.google.dagger:dagger'
     // testAnnotationProcessor 'com.google.dagger:dagger-compiler'
 
+    // Only needed for ModifiedClassPathClassLoader
+    testImplementation(libs.spring5.core)
+
     // JUnit 5
     testImplementation libs.junitJupiter
     testImplementation(libs.archunitJunit5) {