Use dynamic ports in StaticFileMiddlewareTests

[mikeharder]

• Replace hardcoded port "12345" with dynamic ports to improve test reliability
• Addresses https://github.com/aspnet/Home/issues/3063
• Depends on https://github.com/aspnet/Hosting/pull/1387

[mikeharder]

Alternatively, we could add a new public method BuildTestUri(ServerType serverType) to https://github.com/aspnet/Hosting/blob/dev/src/Microsoft.AspNetCore.Server.IntegrationTesting/Common/TestUriHelper.cs, then use this method instead of the private GetTestUrl(). It will be a little more work since it's a new cross-repo API, but it avoids some duplicate code.

[mikeharder]

Even though the methods are public, it turns out no other repos currently use either BuildTestUri() or GetNextPort() from IntegrationTesting (Kestrel has its own copy of GetNextPort():

https://github.com/search?l=C%23&q=org%3Aaspnet+buildtesturi&type=Code https://github.com/search?l=C%23&q=org%3Aaspnet+getnextport&type=Code

So I'm not sure if we want to start the precedent of directly calling either BuildTestUri() or GetNextPort(). We may instead want to make them private in IntegrationTesting.

[mikeharder]

@anurse: Any thoughts regarding whether it's better to share common code like BuildTestUri() and GetNextPort() in integration testing, or just copying the code to repos which need it? It's fairly short and simple code, so I'm not sure if the cross-repo dependency is worth it.

[Tratcher]

Having a dependency for BuildTestUri seems fine, the logic keeps getting more complicated and we only want to maintain it in one place.

[analogrelay]

For repos that already have the dependency sure, I'm not sure it's worth adding new cross-repo dependencies.

[mikeharder]

Ok, I will move the logic to IntegrationTesting and update this PR tomorrow.

[mikeharder]

Updated to use new helper methods added in https://github.com/aspnet/Hosting/pull/1387.