How to use espresso to press a AlertDialog button

According to StackOverflow similar issue: Check if a dialog is displayed with Espresso

You should change your code from:

onView(withText("GA NAAR INSTELLINGEN")).perform(click());

to

onView(withText("GA NAAR INSTELLINGEN")))
    .inRoot(isDialog()) // <---
    .check(matches(isDisplayed()))
    .perform(click());

If it won't work, don't bother to use long with Espresso another great Google's instrumentation test called uiatomator.

Check: http://qathread.blogspot.com/2015/05/espresso-uiautomator-perfect-tandem.html

Example code:

// Initialize UiDevice instance
UiDevice uiDevice = UiDevice.getInstance(InstrumentationRegistry.getInstrumentation());

// Search for correct button in the dialog.
UiObject button = uiDevice.findObject(new UiSelector().text("GA NAAR INSTELLINGEN"));
if (button.exists() && button.isEnabled()) {
    button.click();
}

Hope it will help

Since inRoot(isDialog()) does not seem to work for DialogFragment I use this workaround so far:

enum class AlertDialogButton(@IdRes val resId: Int) {
    POSITIVE(android.R.id.button1),
    NEGATIVE(android.R.id.button2),
    NEUTRAL(android.R.id.button3)
}

fun clickOnButtonInAlertDialog(button: AlertDialogButton) {
    onView(withId(button.resId)).perform(click())
}

For an AlertDialog, the id assigned for each button is:

• POSITIVE: android.R.id.button1
• NEGATIVE: android.R.id.button2
• NEUTRAL: android.R.id.button3

You can check yourself in the AlertController class, setupButtons() method. So you can perform a click as follows:

onView(withId(android.R.id.button1)).perform(click());