Add Transition.progressTo(ContentKey)

            return fromContent == content || toContent == content

        }

        /**

         * Return [progress] if [content] is equal to [toContent], `1f - progress` if [content] is

         * equal to [fromContent], and throw otherwise.

         */

        fun progressTo(content: ContentKey): Float {

            return when (content) {

                toContent -> progress

                fromContent -> 1f - progress

                else ->

                    throw IllegalArgumentException(

                        "content ($content) should be either toContent ($toContent) or " +

                            "fromContent ($fromContent)"

                    )

            }

        }

        /** Run this transition and return once it is finished. */

        abstract suspend fun run()

import kotlinx.coroutines.flow.consumeAsFlow

import kotlinx.coroutines.launch

import kotlinx.coroutines.test.runTest

import org.junit.Assert.assertThrows

import org.junit.Rule

import org.junit.Test

import org.junit.runner.RunWith

        assertThat(state.transitionState).isIdle()

        assertThat(state.transitionState).hasCurrentScene(SceneC)

    }

    @Test

    fun transition_progressTo() {

        val transition = transition(from = SceneA, to = SceneB, progress = { 0.2f })

        assertThat(transition.progressTo(SceneB)).isEqualTo(0.2f)

        assertThat(transition.progressTo(SceneA)).isEqualTo(1f - 0.2f)

        assertThrows(IllegalArgumentException::class.java) { transition.progressTo(SceneC) }

    }

}