Capture behaviour of old diff library

You can see that the diffs were not perfect! If there was no change, double commas showed,
and if there _was_ a diff, ANSI colour codes were only partially removed, leaving behind
a 0x1B ('ANSI Escape') character.

https://en.wikipedia.org/wiki/ANSI_escape_code#C0_control_codes

app/model/commands/UpdateAtomCommand.scala

@@ -11,6 +11,7 @@ import com.gu.media.util.MediaAtomImplicits
 import com.gu.pandomainauth.model.{User => PandaUser}
 import data.DataStores
 import model.commands.CommandExceptions._
+import model.commands.UpdateAtomCommand.createDiffString
 import org.joda.time.DateTime
 import util.AWSConfig
 
@@ -120,7 +121,9 @@ case class UpdateAtomCommand(id: String, atom: MediaAtom, override val stores: D
     val message = AtomAssignedProjectMessage.build(newAtom)
     plutoActions.sendToPluto(message)
   }
+}
 
+object UpdateAtomCommand {
   private val interestingFields = List("title", "category", "description", "duration", "source", "youtubeCategoryId", "license", "commentsEnabled", "channelId", "legallySensitive")
 
   // We don't use HTTP patch so diffing has to be done manually

test/model/commands/UpdateAtomCommandTest.scala

@@ -0,0 +1,57 @@
+package model.commands
+
+import com.gu.media.model.{Category, ContentChangeDetails, MediaAtom}
+import model.commands.UpdateAtomCommand.createDiffString
+import org.scalatest.{FunSuite, MustMatchers}
+
+class UpdateAtomCommandTest extends FunSuite with MustMatchers {
+  val mediaAtomFixture: MediaAtom = MediaAtom(
+    id = "123",
+    labels = List.empty,
+    assets = List.empty,
+    activeVersion = Some(1),
+    title = "title",
+    category = Category.News,
+    description = Some("Example description"),
+    duration = Some(1),
+    source = Some("source"),
+    posterImage = None,
+    trailText = None,
+    youtubeTitle = "title",
+    youtubeDescription = None,
+    trailImage = None,
+    tags = List.empty,
+    byline = List.empty,
+    commissioningDesks = List.empty,
+    contentChangeDetails = ContentChangeDetails(None, None, None, 1L, None, None, None),
+    privacyStatus = None,
+    channelId = None,
+    youtubeCategoryId = None,
+    youtubeOverrideImage = None,
+    keywords = List.empty,
+    license = None,
+    plutoData = None,
+    expiryDate = None,
+    legallySensitive = None,
+    sensitive = None,
+    optimisedForWeb = None,
+    composerCommentsEnabled = None,
+    suppressRelatedContent = None
+  )
+
+  test("Diff output when nothing changes") {
+    createDiffString(mediaAtomFixture, mediaAtomFixture) must be("Updated atom fields (category = News$,, channelId = None,, description = Some( \"Example description\" ),, duration = Some( 1 ),, legallySensitive = None,, license = None,, source = Some( \"source\" ),, title = \"title\",, youtubeCategoryId = None,, youtubeTitle = \"title\")")
+  }
+
+  test("Diff output when description changes") {
+    createDiffString(mediaAtomFixture, mediaAtomFixture.copy(description = Some("New description"))) must be(
+      "Updated atom fields (MediaAtom( ..., description = Some( \u001B\"Example description\"\u001B -> \u001B\"New description\"\u001B ) ))"
+    )
+  }
+
+  test("Diff output when description is removed") {
+    createDiffString(mediaAtomFixture, mediaAtomFixture.copy(description = None)) must be(
+      "Updated atom fields (MediaAtom( ..., description = \u001BSome( \"Example description\" )\u001B -> \u001BNone\u001B ))"
+    )
+  }
+}