title: Solution root could not be located using application root - WebApplicationFactory
body: <p>I am trying to get some tests to properly run in CI using the WebApplicationFactory</p>
  <p>These tests pass locally when we run them through the IDE but they fail with</p>
  <pre><code>System.InvalidOperationException: Solution root could not be located using application root
  </code></pre>
  <p>When we run them in CI.</p>
  <p>In CI, we have a directory called <code>integration_tests</code> which contains multiple <code>dll</code> files for the tests and we run a <code>vstest</code> command to test these dlls, but we do not have the <code>.sln</code> file there.</p>
  <p>Our WebApplicationFactory goes something like this:</p>
  <pre><code>factory = new WebApplicationFactory&lt;Startup&gt;()
                  .WithWebHostBuilder(b =&gt;
                  {
                      b.ConfigureTestServices(s =&gt; {});
                  });
  client = factory.CreateDefaultClient();
  </code></pre>
  <p>I have tried using the <code>WebApplicationFactoryContentRoot</code> and placing it inside the <code>AssemblyInfo.cs</code> but I am unsure that we are using it the right way and I can not find any examples on the docs that actually use it with existing Integration tests.</p>
  <p>I have also tried setting the <code>b.UseSolutionRelativeContentRoot()</code> for the WebHostBuilder, but again, works only locally.</p>
  <p>How can we properly use the <code>WebApplicationFactoryContentRoot</code> to allow the <code>WebApplicationFactory</code> to not only work locally but also in CI for the published dlls?</p>