[Vapor 4.0]How to Write Test Cases to Test Routes That Render Model to Leaf Page

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You want to write test cases for every route right? Yes, I want too. But today, I met a question - How to write test cases to test routes that render model to Leaf page?

We all know testing html is complicated, I want to test the model which will be rendered to the html page, but how?

Let’s see the answer.

First, we need to write our ViewRender, we want to use the custom ViewRender to get the model before it is rendered to html page.

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import Vapor
class CapturingViewRenderer: ViewRenderer {
    var shouldCache = false
    var eventLoop: EventLoop
    init(eventLoop: EventLoop) {
        self.eventLoop = eventLoop
    }
    
    func `for`(_ request: Request) -> ViewRenderer {
        return self
    }

    private(set) var capturedContext: Encodable?
    private(set) var templatePath: String?
    func render<E>(_ name: String, _ context: E) -> EventLoopFuture<View> where E : Encodable {
        self.capturedContext = context
        self.templatePath = name
        let string = "I just want to get the context and the templatePath, I don't care what the view will look like"
        var byteBuffer = ByteBufferAllocator().buffer(capacity: string.count)
        byteBuffer.writeString(string)
        let view = View(data: byteBuffer)
        return eventLoop.future(view)
    }
}

You see, we get the rendering destination templatePath, and the context capturedContext. Maybe you don’t know what context is, just see the route hander, you will undertand.

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func getArticlesHandler(req: Request) throws -> EventLoopFuture<View> {
        return Article.query(on: req.db).all().flatMap {
            return req.view.render("Home",  HomeContext(articles: $0))
        }
    }

The HomeContext is the Context the Leaf framework needs, it wraps our model.

Second, we need to register the ViewRender to our app.

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final class ArticleRoutesTests: XCTestCase {
    var app: Application!
    let url = "/articles"
    let articleName = "Swift"
    let articleBody = "This is my first post"
    var capturingViewRender: CapturingViewRenderer!
    
    override func setUpWithError() throws {
        app = Application(.testing)
        try configure(app)
        capturingViewRender = CapturingViewRenderer(eventLoop: app.eventLoopGroup.next())
        app.views.use {_ in self.capturingViewRender }
    }
		...
}

Third, write the test case to compare the route path and model.

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func testGetArticles() throws {
      try Utils.cleanDatabase(db: app.db)
      let article = Article(name: articleName, body: articleBody)
      try article.save(on: app.db).wait()
      try app.test(.GET, url) { res in
          let context = try XCTUnwrap(capturingViewRender.capturedContext as? ArticleController.HomeContext)
          XCTAssert(capturingViewRender.templatePath == "Home", "render to wrong page")
          XCTAssertTrue(context.articles?.count == 1, "GET /articles api failed.")
          XCTAssertTrue(context.articles?.first?.name == articleName, "GET /articles api failed.")
          XCTAssertTrue(context.articles?.first?.body == articleBody, "GET /articles api failed.")
      }
  }

Done! Enjoy testing.

Thanks to @0xTim for discussion about it.