Testing an application inside docker container in

I'm trying to test an ASP. NET Core 2 dockerized application in VSTS. It is set up inside the docker container via docker-compose. The tests make requests via addresses stored in config (or taken from environment variables, if set).

Right now, the build is set up like this:

Run compose command to restore and publish the app.
Run compose to create and run docker containers.
Run a bash script (explained below).
Run tests.

First of all, I found out that I can't use http://localhost:port inside VSTS. It works fine on my local machine, but it does not work on the server.

I've found this article that points out the need to use container's real IP to access it. I've tried 2 of the methods described in the referenced question, but none of them worked.

When using docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' container_name_or_id, I get Template parsing error: template: :1:24: executing "" at <.NetworkSettings.Net...>: map has no entry for key "NetworkSettings" (the problem is with the command itself)
And when using docker inspect $(sudo docker ps | grep wiremocktest_microservice.gateway | head -c 12) | grep -e \"IPAddress\"\:[[:space:]]\"[0-2] | grep -o '[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}', I actually get the IP and can pass it to tests, but then something strange happens. Namely, they start to time out. I tried to replicate this locally, and it does. Every request that I make to this IP times out (easily checked in browser).

What address do I need to use to access the containers in VSTS, and why can't I use localhost?

I've run into similar problem with having a Azure Storage service running in a container for unit tests (Gradle & Kotlin project). Locally everything's working and it's possible to connect to the container by using localhost:10000 (the port is published to the host machine in run command). But this doesn't work on VSTS build pipeline and neither does when trying to connect with the IP of the container.

I've found a solution that works at least in this case: I created a custom container network and connected my Azure Storage container and the VSTS agent container to that network. After that it's possible to connect to my custom container from the tests by using the container name and internal port number e.g. my-storage-container:10000.

So I created a script that creates the container network, starts my container in that network and then connects also the VSTS agent by grepping the container ID from process list. Its' something like this:

docker network create my-custom-network
docker run --net=my-custom-network -d --name azure-storage-container -t -p 10000:10000 -v ${SCRIPT_DIR}/azurite:/opt/azurite/folder arafato/azurite
CONTAINER_ID=`docker ps -a | awk '{ print $1,$2 }' | grep microsoft/vsts-agent | awk '{print $1 }'`
docker network connect my-custom-network ${CONTAINER_ID}

After that my tests can connect to the Azure storage container with http://azure-storage-container:10000 with no problems.