[2.x] test: Add javaagent test (#9164)

sbt-app/src/sbt-test/tests/javaagent/agent/src/main/scala/JavaAgentMain.java

@@ -0,0 +1,9 @@
+package example;
+
+import java.lang.instrument.Instrumentation;
+
+public class JavaAgentMain {
+    public static void premain(String agentArgs, Instrumentation instrumentation) {
+        new example.A();
+    }
+}

sbt-app/src/sbt-test/tests/javaagent/build.sbt

@@ -0,0 +1,29 @@
+scalaVersion := "2.13.18"
+
+lazy val core = project
+  .settings(
+    libraryDependencies += "org.scalatest" %% "scalatest-funspec" % "3.2.20" % Test,
+    Test / fork := true,
+    Test / classLoaderLayeringStrategy := ClassLoaderLayeringStrategy.Raw,
+    Test / javaOptions += {
+      val agentJar = fileConverter.value.toPath(
+        (agent / Compile / packageBin).value
+      ).toFile.getCanonicalPath
+      s"-javaagent:${agentJar}"
+    }
+  )
+  .dependsOn(agent)
+
+lazy val agent = project
+  .settings(
+    autoScalaLibrary := false,
+    packageOptions += Package.ManifestAttributes(
+      "Premain-Class" -> "example.JavaAgentMain"
+    )
+  )
+  .dependsOn(lib)
+
+lazy val lib = project
+  .settings(
+    autoScalaLibrary := false
+  )

sbt-app/src/sbt-test/tests/javaagent/core/src/test/scala/Test.scala

@@ -0,0 +1,5 @@
+package example
+
+import org.scalatest.funspec.AnyFunSpec
+
+class Test extends AnyFunSpec

sbt-app/src/sbt-test/tests/javaagent/lib/src/main/scala/A.java

@@ -0,0 +1,3 @@
+package example;
+
+public class A {}

sbt-app/src/sbt-test/tests/javaagent/test

@@ -0,0 +1 @@
+> testFull