reading-notes

Read: 31 - Espresso

Espresso

• Espresso code example:

@Test
public void greeterSaysHello() {
    onView(withId(R.id.name_field)).perform(typeText("Steve"));
    onView(withId(R.id.greet_button)).perform(click());
    onView(withText("Hello Steve!")).check(matches(isDisplayed()));
}

• The core API is small, predictable, and easy to learn and yet remains open for customization. Espresso tests state expectations, interactions, and assertions clearly without the distraction of boilerplate content, custom infrastructure, or messy implementation details getting in the way.

• Espresso tests run optimally fast! It lets you leave your waits, syncs, sleeps, and polls behind while it manipulates and asserts on the application UI when it is at rest.

• Espresso is targeted at developers, who believe that automated testing is an integral part of the development lifecycle. While it can be used for black-box testing, Espresso’s full power is unlocked by those who are familiar with the codebase under test.

• Each time your test invokes onView(), Espresso waits to perform the corresponding UI action or assertion until the following synchronization conditions are met:

  1. The message queue is empty.
  2. There are no instances of AsyncTask currently executing a task.
  3. All developer-defined idling resources are idle.

By performing these checks, Espresso substantially increases the likelihood that only one UI action or assertion can occur at any given time. This capability gives you more reliable and dependable test results.

The main components of Espresso:

• Espresso – Entry point to interactions with views (via onView() and onData()). Also exposes APIs that are not necessarily tied to any view, such as pressBack().
• ViewMatchers – A collection of objects that implement the Matcher<? super View> interface. You can pass one or more of these to the onView() method to locate a view within the current view hierarchy.
• ViewActions – A collection of ViewAction objects that can be passed to the ViewInteraction.perform() method, such as click().
• ViewAssertions – A collection of ViewAssertion objects that can be passed the ViewInteraction.check() method. Most of the time, you will use the matches assertion, which uses a View matcher to assert the state of the currently selected view.

find a view

• In the vast majority of cases, the onView() method takes a hamcrest matcher that is expected to match one — and only one — view within the current view hierarchy. Matchers are powerful and will be familiar to those who have used them with Mockito or JUnit.