Add unit tests for areas plugin

game/plugin/areas/src/AreaAction.kt

@@ -0,0 +1,51 @@
+package org.apollo.game.plugins.area
+
+import org.apollo.game.model.Position
+import org.apollo.game.model.entity.Player
+
+/**
+ * A set of actions to execute when a player enters, moves inside, or exits a specific area of the world.
+ */
+internal class AreaAction(val entrance: AreaListener, val inside: AreaListener, val exit: AreaListener)
+
+/**
+ * A function that is invoked when a player enters, moves inside of, or exits an [Area].
+ */
+typealias AreaListener = Player.(Position) -> Unit
+
+/**
+ * Registers an [AreaAction] for the specified [Area] using the builder.
+ */
+fun action(name: String, area: Area, builder: AreaActionBuilder.() -> Unit) {
+    actions += AreaActionBuilder(name, area).apply(builder).build()
+}
+
+/**
+ * Registers an [AreaAction] for the specified [Area] using the builder.
+ *
+ * @param predicate The predicate that determines whether or not the given [Position] is inside the [Area].
+ */
+fun action(name: String, predicate: (Position) -> Boolean, builder: AreaActionBuilder.() -> Unit) {
+    val area = object : Area {
+        override fun contains(position: Position): Boolean = predicate(position)
+    }
+
+    action(name, area, builder)
+}
+
+/**
+ * Registers an [AreaAction] for the specified [Area] using the builder.
+ *
+ * @param x The `x` coordinate range, both ends inclusive.
+ * @param y The `y` coordinate range, both ends inclusive.
+ */
+fun action(name: String, x: IntRange, y: IntRange, height: Int = 0, builder: AreaActionBuilder.() -> Unit) {
+    val area = RectangularArea(x, y, height)
+
+    action(name, area, builder)
+}
+
+/**
+ * The [Set] of ([Area], [AreaAction]) [Pair]s.
+ */
+internal val actions = mutableSetOf<Pair<Area, AreaAction>>()