Some refactor and tests

Tests/EngineTests/EngineTests.swift

@@ -14,7 +14,8 @@ final class EngineTests: XCTestCase {
 				rank -= 1
 			}
 			let pos: Square.Position = .init(rank: rank, file: file)
-			XCTAssertTrue(pos.index == Int(i), "Expected \(i) got \(pos.index!)")
+			XCTAssertTrue(
+				pos.index == Int(i), "Expected \(i) got \(pos.index!)")
 		}
 	}
 	func testDiagonalMoves() throws {
@@ -57,6 +58,53 @@ final class EngineTests: XCTestCase {
 		]
 		XCTAssertEqual(result, r.pseudoLegalPositions)
 	}
+
+	func testKingMoves() throws {
+		let k: King = .init(color: .White, on: .init(rank: 2, file: 8))
+		let result = [
+			Square.Position(rank: 3, file: 8),
+			Square.Position(rank: 1, file: 8),
+			Square.Position(rank: 1, file: 7),
+			Square.Position(rank: 2, file: 7),
+			Square.Position(rank: 3, file: 7),
+		]
+		XCTAssertEqual(result, k.pseudoLegalPositions)
+	}
+
+	func testKnightMoves() throws {
+		let n: Knight = .init(color: .White, on: .init(rank: 4, file: 4))
+		let result = [
+			Square.Position(rank: 6, file: 5),
+			Square.Position(rank: 6, file: 3),
+			Square.Position(rank: 2, file: 5),
+			Square.Position(rank: 2, file: 3),
+			Square.Position(rank: 5, file: 6),
+			Square.Position(rank: 5, file: 2),
+			Square.Position(rank: 3, file: 6),
+			Square.Position(rank: 3, file: 2),
+		]
+		XCTAssertEqual(result, n.pseudoLegalPositions)
+	}
+
+	func testPawnMoves() throws {
+		let pw: Pawn = .init(color: .White, on: .init(rank: 4, file: 4))
+		var result = [
+			Square.Position(rank: 5, file: 4),
+			Square.Position(rank: 6, file: 4),
+			Square.Position(rank: 5, file: 5),
+			Square.Position(rank: 5, file: 3),
+		]
+		XCTAssertEqual(result, pw.pseudoLegalPositions)
+		let pb: Pawn = .init(color: .Black, on: .init(rank: 4, file: 4))
+		result = [
+			Square.Position(rank: 3, file: 4),
+			Square.Position(rank: 2, file: 4),
+			Square.Position(rank: 3, file: 5),
+			Square.Position(rank: 3, file: 3),
+		]
+		XCTAssertEqual(result, pb.pseudoLegalPositions)
+	}
+
 	// func testBoard() throws {
 	// 	let board = Board()
 	// }