Extend scene graph tests

Tests/FirebladeECSTests/Base.swift

@@ -45,6 +45,14 @@ class Color: Component {
     var b: UInt8 = 0
 }
 
+class Index: Component {
+    var index: Int
+
+    init(index: Int) {
+        self.index = index
+    }
+}
+
 final class SingleGameState: SingleComponent {
     var shouldQuit: Bool = false
     var playerHealth: Int = 67

Tests/FirebladeECSTests/SceneGraphTests.swift

@@ -61,7 +61,7 @@ class SceneGraphTests: XCTestCase {
         XCTAssertEqual(nttParrent.numChildren, 0)
     }
 
-    func testDescendRelatives() {
+    func testDescendRelativesSimple() {
         let nttParrent = nexus.createEntity(with: Position(x: 1, y: 1))
         let child1Pos = Position(x: 2, y: 2)
         let nttChild1 = nexus.createEntity(with: child1Pos)
@@ -89,4 +89,39 @@ class SceneGraphTests: XCTestCase {
         XCTAssertEqual(child1Pos.y, 3)
     }
 
+    func testDescendRelativesOnlyFamilyMembers() {
+        let otherComponents: [Component] = [Position(x: 0, y: 0), Velocity(a: 0), Party(partying: true), Color(), Name(name: "")]
+
+        func addChild(to parent: Entity, index: Int) -> Entity {
+            let randComp = otherComponents.randomElement()!
+            let child = nexus.createEntity(with: Index(index: index), randComp)
+            parent.addChild(child)
+            return child
+        }
+
+        let root = nexus.createEntity(with: Index(index: 0))
+
+        var parent: Entity = root
+        for i in 1..<10 {
+            parent = addChild(to: parent, index: i)
+        }
+
+        XCTAssertEqual(nexus.numEntities, 10)
+
+        var parentSum: Int = 0
+        var childSum: Int = 0
+
+        nexus
+            .family(requires: Index.self)
+            .descendRelatives(from: root)
+            .forEach { (parent: Index, child: Index) in
+                XCTAssertEqual(parent.index + 1, child.index)
+                parentSum += parent.index
+                childSum += child.index
+        }
+
+        XCTAssertEqual(parentSum, 36)
+        XCTAssertEqual(childSum, 45)
+    }
+
 }

Tests/FirebladeECSTests/XCTestManifests.swift

@@ -74,7 +74,8 @@ extension SceneGraphTests {
     // to regenerate.
     static let __allTests__SceneGraphTests = [
         ("testAddChild", testAddChild),
-        ("testDescendRelatives", testDescendRelatives),
+        ("testDescendRelativesOnlyFamilyMembers", testDescendRelativesOnlyFamilyMembers),
+        ("testDescendRelativesSimple", testDescendRelativesSimple),
         ("testRemoveAllChildren", testRemoveAllChildren),
         ("testRemoveChild", testRemoveChild)
     ]