Unit Testing a SwiftUI Query

SwiftUIDataUnitTest.swift

//
//  Created by Helge Heß.
//  Copyright © 2023 ZeeZide GmbH.
//

import XCTest
import UIKit
import SwiftData
import SwiftUI

class SwiftUITestCase: XCTestCase {
  
  private lazy var window : UIWindow? = {
    let window = UIWindow(frame: .init(x: 0, y: 0, width: 720, height: 480))
    window.isHidden = false
    return window
  }()
  
  func constructView<V: View>(_ view: V,
                              waitingFor expectation: XCTestExpectation) throws
  {
    let window = try XCTUnwrap(self.window)
    window.rootViewController = UIHostingController(rootView: view)
    window.rootViewController?.view.layoutIfNeeded()
    wait(for: [expectation], timeout: 2)
  }
}

final class SwiftQueryTests: SwiftUITestCase {
  
  @Model
  final class Item {
    var name : String
    init(name: String) { self.name = name }
  }
  
  private let context : ModelContext? = {
    guard let container = try? ModelContainer(
      for: Item.self,
      ModelConfiguration(inMemory: true)
    ) else { return nil }
    let context = ModelContext(container)
    context.insert(Item(name: "One"))
    context.insert(Item(name: "Two"))
    context.insert(Item(name: "Three"))
    return context
  }()
  
  func testFetchCount() throws {
    let context = try XCTUnwrap(context)
    
    class TestResults {
      var fetchedCount = 0
    }
    
    struct TestView: View {
      let results     : TestResults
      let expectation : XCTestExpectation
      
      @Query var values : [ Item ]
      
      var body: Text { // This must NOT be an `EmptyView`!
        results.fetchedCount = values.count
        expectation.fulfill()
        return Text(verbatim: "Dummy")
      }
    }
    
    let expectation = XCTestExpectation(description: "Test Query Count")
    let results = TestResults()
    let view = TestView(results: results, expectation: expectation)
      .modelContext(context)
    
    try constructView(view, waitingFor: expectation)
    
    #if false // this crashes the 15b6 compiler
      XCTAssertEqual(results.fetchedCount, 3)
    #else
      XCTAssertTrue(results.fetchedCount == 3)
    #endif
  }
}