print layer contents in assertion message

Author: dwickern

src/sbt-test/docker-sbt1.0/test-layer-groups-playframework/build.sbt

@@ -30,41 +30,53 @@ enablePlugins(DockerPlugin, LauncherJarPlugin)
 Universal / javaOptions ++= Seq("-J-Xms1024m", "-J-Xmx1024m")
 
 TaskKey[Unit]("checkDockerLayers") := {
-  val layers = (Docker / dockerLayerMappings).value.groupBy(_.layerId).withDefaultValue(Nil)
+  val layerMappings = (Docker / dockerLayerMappings).value
+  val layers = layerMappings.groupBy(_.layerId).withDefaultValue(Nil)
+
+  def printLayers: String = layerMappings.mkString("\n", "\n", "\n")
 
   val layer10 = layers(Some(10))
-  assert(layer10.isEmpty, "layer 10 should be empty because jlink is not used")
+  assert(layer10.isEmpty, s"layer 10 should be empty because jlink is not used: $printLayers")
 
   val layer20 = layers(Some(20))
   assert(
     layer20.forall(_.file.getPath.startsWith(csrCacheDirectory.value.getPath)),
-    "layer 20 should only contain external libraries"
+    s"layer 20 should only contain external libraries: $printLayers"
   )
   assert(
     layer20.exists(_.path == "/opt/docker/lib/org.typelevel.cats-core_2.13-2.13.0.jar"),
-    "layer 20 should contain the common project's dependency"
+    s"layer 20 should contain the common project's dependency: $printLayers"
   )
 
   val layer30 = layers(Some(30))
-  assert(layer30.exists(_.path == "/opt/docker/conf/application.ini"), "layer 30 should contain application.ini")
-  assert(layer30.exists(_.path == "/opt/docker/conf/logback.xml"), "layer 30 should contain logback.xml")
+  assert(
+    layer30.exists(_.path == "/opt/docker/conf/application.ini"),
+    s"layer 30 should contain application.ini: $printLayers"
+  )
+  assert(layer30.exists(_.path == "/opt/docker/conf/logback.xml"), s"layer 30 should contain logback.xml: $printLayers")
 
   val layer40 = layers(Some(40))
   assert(
     layer40.exists(_.file == (Runtime / PlayKeys.playJarSansExternalized).value),
-    "layer 40 should contain Play's -sans-externalized.jar"
+    s"layer 40 should contain Play's -sans-externalized.jar: $printLayers"
   )
-  assert(layer40.exists(_.file == PlayKeys.playPackageAssets.value), "layer 40 should contain Play's -assets.jar")
-  assert(layer40.exists(_.file == packageJavaLauncherJar.value), "layer 40 should contain launcher jar")
+  assert(
+    layer40.exists(_.file == PlayKeys.playPackageAssets.value),
+    s"layer 40 should contain Play's -assets.jar: $printLayers"
+  )
+  assert(layer40.exists(_.file == packageJavaLauncherJar.value), s"layer 40 should contain launcher jar: $printLayers")
   assert(
     layer40.exists(_.file == (common / Compile / packageBin).value),
-    "layer 40 should contain the common project jar"
+    s"layer 40 should contain the common project jar: $printLayers"
   )
   assert(
     layer40.exists(layer => makeBashScripts.value.map(_._1).contains(layer.file)),
-    "layer 40 should contain start scripts"
+    s"layer 40 should contain start scripts: $printLayers"
   )
 
   val layerFinal = layers(None)
-  assert(layerFinal.exists(_.path.startsWith("/opt/docker/share/doc/api/")), "final layer should contain API docs")
+  assert(
+    layerFinal.exists(_.path.startsWith("/opt/docker/share/doc/api/")),
+    s"final layer should contain API docs: $printLayers"
+  )
 }