Initial steps towards running tests in Graalvm (square#6313)

I want to confirm all of OkHttp works with Graalvm, and I'm hoping
to demonstrate that by getting the entire test suite running inside
Graalvm.

square#6296

native-image-tests/README.md

@@ -0,0 +1,55 @@
+Native Image Tests
+==================
+
+This executes OkHttp's test suite inside a Graalvm image.
+
+Seeding Graalvm Config
+----------------------
+
+This isn't yet integrated into the Graalvm Gradle plugin, so you'll need to install your own
+Graalvm and edit `build.gradle` to set its location.
+
+```
+def graalHome = "/Library/Java/JavaVirtualMachines/graalvm-ce-java11-20.2.0/Contents/Home"
+``` 
+
+The task runs tests in the JVM, collecting information about which classes require reflection 
+metadata. This includes the test classes and some parts of the JUnit framework.
+
+```
+./gradlew --info native-image-tests:seedGraalvmConfig
+```
+
+This will create a directory of metadata:
+
+    okhttp
+    '- native-image-tests
+      '- build
+        '- graalvm
+          '- resources
+            '- META-INF
+              '- native-image
+                |- jni-config.json
+                |- proxy-config.json
+                |- reflect-config.json
+                '- resource-config.json
+
+Build the Native Image
+----------------------
+
+Compile the classes and metadata into a Graalvm native image.
+
+```
+./gradlew --info native-image-tests:nativeImage
+```
+
+
+Execute
+-------
+
+The native image runs JUnit 5's `ConsoleLauncher`.
+
+```
+./native-image-tests/build/graal/ConsoleLauncher --select-class okhttp3.SampleTest
+```
+

native-image-tests/build.gradle

@@ -0,0 +1,48 @@
+plugins {
+  id "com.palantir.graal" version "0.7.1"
+}
+
+dependencies {
+  implementation deps.assertj
+  implementation "org.junit.jupiter:junit-jupiter-api:5.7.0"
+  implementation "org.junit.jupiter:junit-jupiter-engine:5.7.0"
+  implementation "org.junit.platform:junit-platform-console:1.7.0"
+
+  compileOnly deps.jsr305
+}
+
+animalsniffer {
+  ignoreFailures = true
+}
+
+def graalHome = "/Library/Java/JavaVirtualMachines/graalvm-ce-java11-20.2.0/Contents/Home"
+def graalvmResources = project.file("$buildDir/graalvm/resources")
+def graalvmConfig = project.file("$graalvmResources/META-INF/native-image")
+graalvmConfig.mkdirs()
+
+sourceSets {
+  main.resources.srcDirs += graalvmResources
+}
+
+task seedGraalvmConfig(type: Exec) {
+  dependsOn("classes")
+  commandLine(
+    "$graalHome/bin/java",
+    "-agentlib:native-image-agent=config-output-dir=$graalvmConfig",
+    "-classpath", sourceSets.main.runtimeClasspath.getAsPath(),
+    "org.junit.platform.console.ConsoleLauncher",
+    "--select-class", "okhttp3.SampleTest"
+  )
+}
+
+graal {
+  mainClass "org.junit.platform.console.ConsoleLauncher"
+  outputName "ConsoleLauncher"
+  graalVersion "20.2.0"
+  javaVersion "11"
+
+  option "--enable-https"
+  option "--no-fallback"
+  option "--allow-incomplete-classpath"
+  option "--report-unsupported-elements-at-runtime"
+}

native-image-tests/src/main/kotlin/okhttp3/SampleTest.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2020 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package okhttp3
+
+import org.assertj.core.api.AssertionsForClassTypes.assertThat
+import org.junit.jupiter.api.Test
+
+class SampleTest {
+  @Test
+  fun failingTest() {
+    assertThat("hello").isEqualTo("goodbye")
+  }
+}

settings.gradle

@@ -8,6 +8,7 @@ if (properties.containsKey('android.injected.invoked.from.ide') ||
   include ':android-test'
 }
 
+include ':native-image-tests'
 include ':okcurl'
 include ':okhttp'
 include ':okhttp-bom'