Add tests for docker module

Add tests for a docker config with defaults (no options) and
all options specified by building them.

build.sc

@@ -579,9 +579,13 @@ object contrib extends MillModule {
     override def ivyDeps = Agg(Deps.flywayCore)
   }
 
-
   object docker extends MillModule {
     override def compileModuleDeps = Seq(scalalib)
+    override def testArgs = T {
+      Seq("-Djna.nosys=true") ++
+        scalalib.worker.testArgs() ++
+        scalalib.backgroundwrapper.testArgs()
+    }
   }
 
   object bloop extends MillModule {

contrib/docker/test/resources/docker/src/Main.scala

@@ -0,0 +1 @@
+object Main extends App

contrib/docker/test/src/DockerModuleTest.scala

@@ -0,0 +1,114 @@
+package mill
+package contrib.docker
+
+import mill.api.PathRef
+import mill.scalalib.JavaModule
+import mill.util.{TestEvaluator, TestUtil}
+import os.Path
+import utest._
+import utest.framework.TestPath
+
+object DockerModuleTest extends TestSuite {
+
+  object Docker extends TestUtil.BaseModule with JavaModule with DockerModule {
+
+    override def millSourcePath = TestUtil.getSrcPathStatic()
+    override def artifactName = testArtifactName
+
+    object dockerDefault extends DockerConfig
+
+    object dockerAll extends DockerConfig {
+      override def baseImage = "openjdk:11"
+      override def labels = Map("version" -> "1.0")
+      override def exposedPorts = Seq(8080, 443)
+      override def exposedUdpPorts = Seq(80)
+      override def volumes = Seq("/v1", "/v2")
+      override def envVars = Map("foo" -> "bar", "foobar" -> "barfoo")
+      override def run = Seq(
+        "/bin/bash -c 'echo Hello World!'",
+        "useradd -ms /bin/bash user1"
+      )
+      override def user = "user1"
+    }
+  }
+
+  val testArtifactName = "mill-docker-contrib-test"
+
+  val testModuleSourcesPath: Path =
+    os.pwd / "contrib" / "docker" / "test" / "resources" / "docker"
+
+  private def isInstalled(executable: String): Boolean = {
+    val getPathCmd = if (scala.util.Properties.isWin) "where" else "which"
+    os.proc(getPathCmd, executable).call(check = false).exitCode == 0
+  }
+
+  private def workspaceTest(m: TestUtil.BaseModule)(t: TestEvaluator => Unit)(
+      implicit tp: TestPath
+  ): Unit = {
+    if (isInstalled("docker")) {
+      val eval = new TestEvaluator(m)
+      os.remove.all(m.millSourcePath)
+      os.remove.all(eval.outPath)
+      os.makeDir.all(m.millSourcePath / os.up)
+      os.copy(testModuleSourcesPath, m.millSourcePath)
+      t(eval)
+    } else assert(true)
+  }
+
+  override def utestAfterAll(): Unit = {
+    if (isInstalled("docker"))
+      os
+        .proc("docker", "rmi", testArtifactName)
+        .call(stdout = os.Inherit, stderr = os.Inherit)
+    else ()
+  }
+
+  def tests = Tests {
+
+    test("docker build") {
+      "default options" - workspaceTest(Docker) { eval =>
+        val Right((imageName :: Nil, _)) = eval(Docker.dockerDefault.build)
+        assert(imageName == testArtifactName)
+      }
+
+      "all options" - workspaceTest(Docker) { eval =>
+        val Right((imageName :: Nil, _)) = eval(Docker.dockerAll.build)
+        assert(imageName == testArtifactName)
+      }
+    }
+
+    test("dockerfile contents") {
+      "default options" - {
+        val eval = new TestEvaluator(Docker)
+        val Right((dockerfileString, _)) = eval(Docker.dockerDefault.dockerfile)
+        val expected =
+          """
+            |FROM gcr.io/distroless/java:latest
+            |
+            |COPY out.jar /out.jar
+            |ENTRYPOINT ["java", "-jar", "/out.jar"]""".stripMargin
+        assert(dockerfileString == expected)
+      }
+
+      "all options" - {
+        val eval = new TestEvaluator(Docker)
+        val Right((dockerfileString, _)) = eval(Docker.dockerAll.dockerfile)
+        val expected =
+          """
+            |FROM openjdk:11
+            |LABEL "version"="1.0"
+            |EXPOSE 8080/tcp 443/tcp
+            |EXPOSE 80/udp
+            |ENV foo=bar
+            |ENV foobar=barfoo
+            |VOLUME ["/v1", "/v2"]
+            |RUN /bin/bash -c 'echo Hello World!'
+            |RUN useradd -ms /bin/bash user1
+            |USER user1
+            |COPY out.jar /out.jar
+            |ENTRYPOINT ["java", "-jar", "/out.jar"]""".stripMargin
+        assert(dockerfileString == expected)
+      }
+    }
+  }
+}