[Math] Some basic Vector tests

Math/MathTests/MatrixFunctionalTests.swift

@@ -8,7 +8,23 @@
 
 import Foundation
 import XCTest
+@testable import Math
+
+func assertVectorAlmostEqual<T: Vector>(@autoclosure lhs: () -> T?, @autoclosure _ rhs: () -> T?, message: String = "", file: String = __FILE__, line: UInt = __LINE__) {
+    let lhsValue = lhs()
+    let rhsValue = rhs()
+    let msg = message != "" ? message : "expected \(lhsValue), got \(rhsValue)"
+    XCTAssert(lhsValue ==~ rhsValue, msg, file: file, line: line)
+}
 
 class MatrixVectorTests: XCTestCase {
-    func 
+    func testThatMultiplyingIdentityByAVectorGivesTheVector() {
+        let v = Matrix4.identity * Vector4(x: 1, y: 2, z: 3)
+        assertVectorAlmostEqual(v, Vector4(x: 1, y: 2, z: 3))
+    }
+
+    func testThatMultiplyingTranslationByAVectorGivesTranslatedVector() {
+        let v = Matrix4(translationWithX: 1, y: 1, z: 1) * Vector4(x: 2, y: 2, z: 2)
+        assertVectorAlmostEqual(v, Vector4(x: 3, y: 3, z: 3))
+    }
 }