Working With the REPL

PDF for offline use:

Let us know how you feel about this.

Thanks for the feedback!

last updated: 2016-10


One of the important tools in creating UITests is the the REPL (read-eval-print-loop). The REPL is a console-like environment in which the developer enters expressions or a commands. It will then evaluate those expressions, and display the results to the user.

The REPL is helpful when creating UITests – it allows us to explore the user interface and create the queries and statements so that the test may interact with the application.

Starting the REPL

The REPL can only be started by running a test which calls the IApp.Repl() method:

public class Tests
    AndroidApp app;

    public void BeforeEachTest()
        app = ConfigureApp.Android.StartApp();

    public void CreditCardNumber_TooShort_DisplayErrorMessage()

When the test is run and .Repl() is invoked, UITest will halt the test and start the REPL in a terminal window:

There are three ways to exit the REPL:

  • Pressing Ctrl-C
  • Typing exit
  • Typing quit

UITest will resume executing the rest of the test when the REPL is closed.

Using the REPL

The REPL provides an instance of IApp that will allow interaction with the application. The REPL also provides two commands that are useful for creating UITests, the tree command and the copy command.

A common workflow is to use the tree command or IApp.Flash to identify views on the screen and to obtain meta-data about those views. That information is used to to create AppQueries and spike out the steps that will make up a test. Then the copy command can be used to copy that work to the clipboard so that it may be pasted into the test.

Discovering Views With the tree Command

The tree command will display a hierarchical list of the views that are visible on the screen:

Discovering Views with IApp.Flash

Many of the UITest API's take an AppQuery object to locate views on the screen. The IApp.Flash() method can be very helpful in testing these queries in the REPL. IApp.Flash() will highlight the results of the query by making them flash, and return some details about the views in the results.

As an example, the following snippet shows how we can locate all of the EditText views that are visible on an Android activity:

>>> app.Flash(c=>c.Class("EditText"))                               
Flashing query for Class("EditText") gave 1 results.
    "Id": "creditCardNumberText",
    "Description": "android.widget.EditText{528165e4 VFED..CL .F...... 139,70-941,178 #7f050001 app:id/creditCardNumberText}",
    "Rect": {
      "Width": 802.0,
      "Height": 108.0,
      "X": 139.0,
      "Y": 274.0,
      "CenterX": 540.0,
      "CenterY": 328.0
    "Label": null,
    "Text": "",
    "Class": "android.widget.EditText",
    "Enabled": true

We can use the Flash method to help create AppQuerys to use in conjunction with the other APIs to work out a test.

Creating Steps in a Test

Let's see how we can use the REPL to quickly test out individual steps in a test without having to compile the application, deploy it to a device/simulator/emulator, and then run the application – a very time consuming process.

As an example, we can use the results of the tree command above. If our test is required to enter text in the EditText with the ID of creditCardNumberText, it could use the IApp.EnterText method:

>>> app.EnterText(c=>c.Marked("creditCardNumberText"), "1234567890123456")
Using element matching Marked("creditCardNumberText").
Tapping coordinates [ 540, 328 ].

Likewise, if the test needs to simulate the user tapping on a button, it could use the IApp.Tap method:

>>> app.Tap(c=>c.Marked("validateButton"))
Using element matching Marked("validateButton").
Tapping coordinates [ 540, 533 ].

Using the copy Command

The REPL will keep a history of the commands that you have entered into it during the session. The copy command paste those commands into the clipboard:

>>> copy
Copying history to clipboard.

This allows you to test out and debug commands in the REPL, and then promptly update your test code.


In this guide we discussed how to use the REPL to help create UITests. We discussed how to start and stop the REPL, Other th and how to build out the steps that make up a UITest.

Xamarin Workbook

If it's not already installed, install the Xamarin Workbooks app first. The workbook file should download automatically, but if it doesn't, just click to start the workbook download manually.