The documentation talks about dependency injection but does not really show how it is being done.

Documentation is not completed as well and has a bunch of place holders: http://ktor.io/getting-started.html

I tried to create my main function in a way that it accepts parameter (which is my dependency) but that failed on the test side when I call withTestApplication. I looked into the application code and saw that Application accepts a configuration object but I have no idea how I can change that configuration object to inject some dependencies inside of it.

package org.jetbrains.ktor.application

/**
 * Represents configured and running web application, capable of handling requests
 */
class Application(val environment: ApplicationEnvironment) : ApplicationCallPipeline() {
    /**
     * Called by host when [Application] is terminated
     */
    fun dispose() {
        uninstallAllFeatures()
    }
}

/**
 * Convenience property to access log from application
 */
val Application.log get() = environment.log

In the test code using withTestApplication I have something similar to the below:

@Test
internal fun myTest() = withTestApplication (Application::myMain)

The above withTestApplication would fail if I call myMain with parameters (parameters that I need to mock and inject.)

Update:

The issue is that in my request handling, I am using a dependency class that connects to other web services outside and does some requests, I need a way to be able to inject this so in my tests I can stub/mock it and change its behavior based on my test cases.