test: make Solr version configurable for compatibility testing (#50)

Author: adityamparikh

AGENTS.md

@@ -73,6 +73,27 @@ Spring Boot Buildpacks output logs to stdout, breaking MCP's STDIO protocol. Jib
 - **Integration tests** (`*IntegrationTest.java`, `*DirectTest.java`): Real Solr via Testcontainers
 - **Docker tests** (`containerization/`): Tagged `@Tag("docker-integration")`, run separately
 
+### Solr Version Compatibility Testing
+
+The Solr Docker image used in tests is configurable via the `solr.test.image` system property (default: `solr:9.9-slim`):
+
+```bash
+./gradlew test -Dsolr.test.image=solr:8.11-slim    # Solr 8.11
+./gradlew test -Dsolr.test.image=solr:9.4-slim     # Solr 9.4
+./gradlew test -Dsolr.test.image=solr:9.9-slim     # Solr 9.9 (default)
+```
+
+**Tested compatible versions:** 8.11, 9.4, 9.9
+
+### Solr 10 Compatibility Notes
+
+Solr 10 introduces breaking changes that will require updates to this project:
+
+- **MBeans removal:** `SolrInfoMBeanHandler` is removed. `CollectionService.getCollectionStats()` uses `/admin/mbeans` for cache and handler metrics — this will need to migrate to the `/admin/metrics` endpoint or OpenTelemetry.
+- **Metrics migration:** Dropwizard metrics replaced by OpenTelemetry. All metric names switch to snake_case. JMX, Prometheus exporter, SLF4J, and Graphite reporters are removed.
+- **SolrJ base URL:** SolrClient now only accepts root URLs (e.g., `http://host:8983/solr`). This project already uses root URLs with per-request collection names, so **no change needed** here.
+- **SolrJ dependency:** Upgrade `solr-solrj` from 9.x to 10.x in `gradle/libs.versions.toml`. The Jetty BOM alignment (`jetty = "10.0.22"`) will also need updating since Solr 10 uses Jetty 12.x.
+
 ## Key Configuration
 
 Environment variables:

build.gradle.kts

@@ -153,6 +153,8 @@ tasks.withType<Test> {
             excludeTags("docker-integration")
         }
     }
+    // Forward solr.test.image system property to test JVMs for Solr version compatibility testing
+    systemProperty("solr.test.image", System.getProperty("solr.test.image", "solr:9.9-slim"))
     if (name != "dockerIntegrationTest") {
         finalizedBy(tasks.jacocoTestReport)
     }

src/test/java/org/apache/solr/mcp/server/TestcontainersConfiguration.java

@@ -29,7 +29,8 @@ public class TestcontainersConfiguration {
 
 	@Bean
 	SolrContainer solr() {
-		return new SolrContainer(DockerImageName.parse("solr:9.9-slim"));
+		String solrImage = System.getProperty("solr.test.image");
+		return new SolrContainer(DockerImageName.parse(solrImage));
 	}
 
 	@Bean

src/test/java/org/apache/solr/mcp/server/containerization/DockerImageHttpIntegrationTest.java

@@ -95,7 +95,7 @@ class DockerImageHttpIntegrationTest {
 
 	// Docker image name and tag from build-info.properties
 	private static final String DOCKER_IMAGE = BuildInfoReader.getDockerImageName();
-	private static final String SOLR_IMAGE = "solr:9.9-slim";
+	private static final String SOLR_IMAGE = System.getProperty("solr.test.image");
 	private static final int HTTP_PORT = 8080;
 
 	// Network for container communication

src/test/java/org/apache/solr/mcp/server/containerization/DockerImageStdioIntegrationTest.java

@@ -85,7 +85,7 @@ class DockerImageStdioIntegrationTest {
 
 	// Docker image name and tag from build-info.properties
 	private static final String DOCKER_IMAGE = BuildInfoReader.getDockerImageName();
-	private static final String SOLR_IMAGE = "solr:9.9-slim";
+	private static final String SOLR_IMAGE = System.getProperty("solr.test.image");
 
 	// Network for container communication
 	private static final Network network = Network.newNetwork();