How do I assert that a scrollable TabLayout is currently showing a certain tab?

Question

I am displaying a TabLayout and connecting it to a ViewPager2 object (by means of the TabLayoutMediator class). The TabLayout has a tabMode of scrollable and contains more tabs than can fit in the screen at once. I want to assert that a certain one of the tabs is visible and selected when my activity or fragment is rendered. How do I do this?

Answer 1

You can create a custom Matcher for the tabs:

fun withTab(title: String) = withTab(equalTo(title))

fun withTab(title: Matcher<String>): Matcher<View> {
    return object : BoundedMatcher<View, TabView>(TabView::class.java) {
        override fun describeTo(description: Description) {
            description.appendText("with tab: ")
            title.describeTo(description)
        }

        override fun matchesSafely(item: TabView): Boolean {
            return title.matches(item.tab?.text)
        }
    }
}

Then to find if a tab is currently showing, you can conveniently do it with:

onView(withTab("tab text")).check(matches(isCompletelyDisplayed()))

If you want to assert if a tab is currently selected, you can either adjust matchesSafely to work with item.tab?.isSelected, or simply create a new matcher.

However if you have more than one TabLayout on the screen, then you may need to composite your matcher with isDescendantOfA or withParent.