Some improvements

Tests/xpmkitTests/Linter/GraphLinterTests.swift

@@ -0,0 +1,13 @@
+import Basic
+import Foundation
+import XCTest
+@testable import xpmkit
+
+final class GraphLinterTests: XCTestCase {
+    var subject: GraphLinter!
+
+    override func setUp() {
+        super.setUp()
+        subject = GraphLinter()
+    }
+}