Question

I wrote the following code:

[TestMethod]
//[ExpectedException(typeof(UriFormatException), "url should be well formatted.")]
public void FetchHtmlContent_badUrl_throwUriFormatException()
{
    HashSet<string> urls = new HashSet<string> { "ww.stackoverflow.com" };
    var contextManager = new ContentManager(urls);
    var content = contextManager.GetHtmlContent();
    Assert.IsTrue(content.ElementAt(0).Contains("threw an exception of type 'System.UriFormatException'"));
}

contextManager.GetHtmlContent() doesn’t throw an exception,

but content.ElementAt(0) throws (as expected)

+       content.ElementAt(0)    'content.ElementAt(0)' threw an exception of type 'System.UriFormatException'   string {System.UriFormatException}

How can I verify content.ElementAt(0) throws this exception

(or should I verify this test some other way ?)

Answer 1

What’s the responsibility of the ContentManager.GetHtmlContent method? If as name would indicate, retrieving HTML content from URL, then invalid url is execution failure scenario (method cannot do what it is supposed to). You have two choices:

• throw invalid uri Exception from .GetHtmlContent method (communicates well what happens, and follows Microsoft guidelines)
• return null from .GetHtmlContent and deal with that later

Note that returning null result might also be used for a case when HTML content is indeed null, therefore I suggest throwing exception here. It states what happened in more clear way.

Your test might look like that:

[TestMethod]
[ExpectedException(typeof(UriFormatException), "url should be well formatted.")]
public void GetHtmlContent_ThrowsInvalidUriException_WhenUriIsInBadFormat()
{
    HashSet<string> urls = new HashSet<string> { "ww.stackoverflow.com" };
    var contextManager = new ContentManager(urls);

    contextManager.GetHtmlContent();
}