Add a couple of missing test stub files

Author: mattpolzin

Tests/OpenAPIKitTests/Path Item/OperationTests.swift

@@ -0,0 +1,13 @@
+//
+//  OperationTests.swift
+//  
+//
+//  Created by Mathew Polzin on 12/29/19.
+//
+
+import XCTest
+import OpenAPIKit
+
+final class OperationTests: XCTestCase {
+    // TODO: write tests
+}

Tests/OpenAPIKitTests/Path Item/ParameterTests.swift

@@ -0,0 +1,13 @@
+//
+//  ParameterTests.swift
+//  
+//
+//  Created by Mathew Polzin on 12/29/19.
+//
+
+import XCTest
+import OpenAPIKit
+
+final class ParameterTests: XCTestCase {
+    // TODO: write tests
+}