Archive for the 'Software Engineering' Category



ScalaMock 3.0-M4 for Scala 2.10.0-RC1

ScalaMock 3.0-M4 (scaladoc) for Scala 2.10.0-RC1 is now released. It supports:

  • Mock functions, traits and classes
  • Both expectation-first and record-then-verify (Mockito-style) mocking
  • ScalaTest and Specs2

To use with sbt and ScalaTest:

libraryDependencies +=
  "org.scalamock" % "scalamock-scalatest-support_2.10.0-RC1" % "3.0-M4"

or for Specs2:

libraryDependencies +=
  "org.scalamock" % "scalamock-specs2-support_2.10.0-RC1" % "3.0-M4"

For background information, see ScalaMock 3.0 Preview Release.

Known limitations (these should all be fixed when Scala adds support for mock types):

  • No support for mocking object creation (constructors)
  • No support for mocking singleton/companion objects
  • No support for mocking final classes or classes with private constructors
  • No support for mocking concrete vars
  • Limited support for overloaded methods
  • No support for mocking Java methods with repeated parameters

ScalaMock 3.0-M1

ScalaMock 3.0-M1 (scaladoc) for Scala 2.10.0-M4 is now released. It supports:

  • Mock functions, traits and classes
  • Both expectation-first and record-then-verify (Mockito-style) mocking
  • ScalaTest and Specs2

To use with sbt:

libraryDependencies +=
  "org.scalamock" %% "scalamock-scalatest-support" % "3.0-M1"

For background information, see ScalaMock 3.0 Preview Release.

It’s been tested against overloaded, curried and polymorphic methods, by-name parameters, path-dependent types and type projections. There may still be corner cases that aren’t handled correctly, please report a bug if you find one.

ScalaMock 3.0 Preview Release

Update: ScalaMock 3.0-M4 for Scala 2.10.0-RC1 is now released.

The current version of ScalaMock makes use of a compiler plugin to generate typesafe mock objects. This works, but has a number of problems, not least of which is the complicated nature of the build system required (meaning that it currently only works with sbt). The recent preview release of Scala 2.10 has opened up a new approach via its support for macros.

I’ve just released a preview of ScalaMock 3.0, a “from the ground up” rewrite using macros. It’s not yet as capable as ScalaMock 2.x (it can only mock traits – there’s no support for mocking classes, singleton/companion objects or object creation yet) but it’s certainly complete enough to be useful, I hope.

One significant (and frequently requested!) enhancement over ScalaMock 2.x is support for Mockito-style “record then verify” mocking as well as the more traditional “setup expectations” style.

The source is available on GitHub, and a snapshot release (Scala 2.10.0-M3 only) is available on Sonatype:

libraryDependencies +=
  "org.scalamock" %% "scalamock-scalatest-support" % "3.0-SNAPSHOT"

You can see examples of it in use in GitHub.

Here’s an example of a test written using the “setup expectations” style:

class ControllerTest extends FunSuite with MockFactory {

  test("draw line") {
    val mockTurtle = mock[Turtle]
    val controller = new Controller(mockTurtle)

    inSequence {
      inAnyOrder {
        (mockTurtle.penUp _) expects ()
        (mockTurtle.getPosition _) expects () returning (0.0, 0.0)
        (mockTurtle.getAngle _) expects () returning 0.0
      }
      (mockTurtle.turn _) expects ~(Pi / 4)
      (mockTurtle.forward _) expects ~sqrt(2.0)
      (mockTurtle.getAngle _) expects () returning Pi / 4
      (mockTurtle.turn _) expects ~(-Pi / 4)
      (mockTurtle.penDown _) expects ()
      (mockTurtle.forward _) expects 1.0
    }

    controller.drawLine((1.0, 1.0), (2.0, 1.0))
  }
}

and here’s the same example rewritten to use the Mockito-style record and then verify approach:

class ControllerTest extends FunSuite with MockFactory {
  import scala.language.postfixOps

  test("draw line") {
    val mockTurtle = stub[Turtle]
    val controller = new Controller(mockTurtle)

    inSequence {
      inAnyOrder {
        (mockTurtle.getPosition _) when () returns (0.0, 0.0)
        (mockTurtle.getAngle _) when () returns 0.0 once
      }
      (mockTurtle.getAngle _) when () returns Pi / 4
    }

    controller.drawLine((1.0, 1.0), (2.0, 1.0))

    inSequence {
      (mockTurtle.turn _) verify ~(Pi / 4)
      (mockTurtle.forward _) verify ~sqrt(2.0)
      (mockTurtle.turn _) verify ~(-Pi / 4)
      (mockTurtle.penDown _) verify ()
      (mockTurtle.forward _) verify 1.0
    }
  }
}

Right now, it supports:

  • Mock functions (including higher-order functions)
  • Polymorphic traits
  • Polymorphic methods
  • Curried methods
  • Overloaded methods

Here’s my todo list:

  • Sort out the documentation
  • Take advantage of macro types (type providers) when available in a subsequent Scala release. This will enable a slightly nicer syntax for method mocking:

    mockObject.expects.method(arguments)

    instead of:

    (mockObject.method _) expects (arguments)

  • Mocking classes (as well as traits)
  • Mocking singleton/companion objects
  • Mocking object creation

I’d be very grateful for any feedback, in particular bug reports.

Mockito on Android step-by-step

One of my biggest frustrations with writing code for Android has been the fact that none of the current Java mocking frameworks work on Android’s Dalvik VM. I tried to address that myself by getting ScalaMock working on Android, but that’s been less successful than I hoped (primarily due to general problems with getting Scala working in the Android environment).

Happily there’s been a major breakthrough recently – Mockito, one of the established Java mocking frameworks now supports Android 🙂 In this article, I’ll go through getting an Android application up and running with tests written using Mockito.

This is an Android version of the example in Martin Fowler’s article Mocks Aren’t Stubs. The code is checked into GitHub here. You’ll need to have the Android SDK and ADT Plugin for Eclipse installed to run this code.

We’re going to build a (very) simple ordering system. Orders will succeed if there’s enough inventory in our warehouse and fail if not. Let’s start by creating a very simple little Android application for us to test:

  1. Create a new Android project in Eclipse called WarehouseManager. Select the “Create a Test Project” option.
  2. The core abstraction is a warehouse, represented by a Warehouse interface:

    package com.example;
    
    public interface Warehouse {
        boolean hasInventory(String product, int quantity);
        void remove(String product, int quantity);
    }
  3. And here’s a very simple concrete implementation of Warehouse:

    package com.example;
    
    import java.util.HashMap;
    
    public class RealWarehouse implements Warehouse {
    
        public RealWarehouse() {
            products = new HashMap();
            products.put("Talisker", 5);
            products.put("Lagavulin", 2);
        }
    
        public boolean hasInventory(String product, int quantity) {
            return inStock(product) >= quantity;
        }
    
        public void remove(String product, int quantity) {
            products.put(product, inStock(product) - quantity);
        }
    
        private int inStock(String product) {
            Integer quantity = products.get(product);
            return quantity == null ? 0 : quantity;
        }
    
        private HashMap products;
    }
  4. We remove things from the warehouse by placing an Order:

    package com.example;
    
    public class Order {
    
        public Order(String product, int quantity) {
            this.product = product;
            this.quantity = quantity;
        }
    
        public void fill(Warehouse warehouse) {
            if (warehouse.hasInventory(product, quantity)) {
                warehouse.remove(product, quantity);
                filled = true;
            }
        }
    
        public boolean isFilled() {
            return filled;
        }
    
        private boolean filled = false;
        private String product;
        private int quantity;
    }
  5. We’ll need a UI to allow us to make orders, so modify main.xml to look like this:

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        >
      <TextView  
          android:layout_width="fill_parent" 
          android:layout_height="wrap_content" 
          android:text="Product:"
          />
      <EditText
          android:layout_width="fill_parent" 
          android:layout_height="wrap_content"
          android:id="@+id/product"
          />
      <TextView
          android:layout_width="fill_parent" 
          android:layout_height="wrap_content" 
          android:text="Quantity:"
          />
      <EditText
          android:layout_width="fill_parent" 
          android:layout_height="wrap_content"
          android:id="@+id/quantity"
          />
      <Button
          android:layout_height="wrap_content"
          android:layout_width="wrap_content"
          android:text="Place order"
          android:onClick="placeOrder" />
    </LinearLayout>
  6. And finally, here’s the implementation of WarehouseManagerActivity:

    package com.example;
    
    import android.app.Activity;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.EditText;
    import android.widget.Toast;
    
    public class WarehouseManagerActivity extends Activity {
        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
    
            productEditText = (EditText)findViewById(R.id.product);
            quantityEditText = (EditText)findViewById(R.id.quantity);
        }
    
        public void placeOrder(View view) {
            String product = productEditText.getText().toString();
            int quantity = Integer.parseInt(quantityEditText.getText().toString());
            Order order = new Order(product, quantity);
            order.fill(warehouse);
    
            String message = order.isFilled() ? "Success" : "Failure";
            Toast toast = Toast.makeText(this, message, Toast.LENGTH_SHORT);
            toast.show();
        }
    
        private Warehouse warehouse = new RealWarehouse();
    
        private EditText productEditText;
        private EditText quantityEditText;
    }

You should now have a little Android application that can be compiled and installed with ant install. Here’s what it looks like:

Screenshot

So, now that we’ve got something to test, let’s test it:

  1. The version of Mockito that supports Android has not yet been released, so you’ll need to get the source and build it for yourself. After building, you should have mockito-all-1.9.1-SNAPSHOT.jar in the target directory.
  2. Create a libs directory underneath WarehouseManagerTest and copy mockito-all-1.9.1-SNAPSHOT.jar into it. Download the latest dexmaker into the same directory.
  3. Finally, we can write our tests, which create mock instances of the Warehouse interface:

    package com.example.test;
    
    import android.test.InstrumentationTestCase;
    import com.example.*;
    
    import static org.mockito.Mockito.*;
    
    public class OrderTest extends InstrumentationTestCase {
    
        public void testInStock() {
            Warehouse mockWarehouse = mock(Warehouse.class);
    
            when(mockWarehouse.hasInventory("Talisker", 50)).thenReturn(true);
    
            Order order = new Order("Talisker", 50);
            order.fill(mockWarehouse);
    
            assertTrue(order.isFilled());
            verify(mockWarehouse).remove("Talisker", 50);
        }
    
        public void testOutOfStock() {
            Warehouse mockWarehouse = mock(Warehouse.class);
    
            when(mockWarehouse.hasInventory("Talisker", 50)).thenReturn(false);
    
            Order order = new Order("Talisker", 50);
            order.fill(mockWarehouse);
    
            assertFalse(order.isFilled());
        }
    }
  4. Run your tests 🙂

ScalaMock 2.2

I’ve just released ScalaMock 2.2, with the following improvements over 2.1:

  • Add support for repeated parameters (varargs)
  • Basic parameterised class support

ScalaMock is a native Scala mocking framework which, as well as traits (interfaces) and functions, can also mock:

  • Classes
  • Singleton and companion objects (static methods)
  • Object creation (constructor invocation)
  • Polymorphic (type parameterised) methods
  • Classes with private constructors
  • Final classes and classes with final methods
  • Operators (methods with symbolic names)
  • Overloaded methods

ScalaMock 2.1

I’ve just released ScalaMock 2.1, with the following improvements over 2.0:

  • Add support for polymorphic (type parameterised) methods
  • Add support for curried methods
  • Fix String constants in Java classes
  • Fix unmocked operators

ScalaMock is a native Scala mocking framework which, as well as traits (interfaces) and functions, can also mock:

  • Classes
  • Singleton and companion objects (static methods)
  • Object creation (constructor invocation)
  • Polymorphic (type parameterised) methods
  • Classes with private constructors
  • Final classes and classes with final methods
  • Operators (methods with symbolic names)
  • Overloaded methods

ScalaMock step-by-step

This post describes ScalaMock 2, which is no longer under development. For the current development version, go here.

ScalaMock (previously Borachio) is a mocking library for Scala. As well as traits (interfaces) and functions, it can also mock:

  • Classes
  • Singleton and companion objects (static methods)
  • Object creation (constructor invocation)
  • Classes with private constructors
  • Final classes and classes with final methods
  • Operators (methods with symbolic names)
  • Overloaded methods

This post describes how to setup a project that uses ScalaMock in conjunction with ScalaTest and sbt 0.11. The sample code described in this article is available on GitHub.

Note: If you only want to mock functions and traits (interfaces), you can use ScalaMock’s proxy mocks by simply linking with the .jar file – no need to use the compiler plugin or sbt plugin described below.

The example assumes that we’re writing code to control a mechanical turtle, similar to that used by Logo programs. Mocking is useful in this kind of situation because we might want to create tests that function even if we don’t have the hardware to hand, which run more quickly than would be the case if we ran on real hardware, and where we can use mocks to simulate errors or other situations difficult to reproduce on demand.

Getting started

  1. Create a root directory for your project:
    $ mkdir myproject
  2. ScalaMock uses a compiler plugin to generate code. There’s an sbt plugin that makes setting this up easy. Add this plugin to your project by creating project/project/Build.scala containing:
    import sbt._
    object PluginDef extends Build {
      override lazy val projects = Seq(root)
      lazy val root = Project("plugins", file(".")) dependsOn(scalamockPlugin)
      lazy val scalamockPlugin = uri("git://github.com/paulbutcher/scalamock-sbt-plugin")
    }
  3. Create project/Build.scala containing:
    import sbt._
    import Keys._
    import ScalaMockPlugin._
    
    object MyBuild extends Build {
    
      override lazy val settings = super.settings ++ Seq(
        organization := "com.example",
        version := "1.0",
        scalaVersion := "2.9.1",
    
        resolvers += ScalaToolsSnapshots,
        libraryDependencies += "org.scalamock" %% "scalamock-scalatest-support" % "2.0-SNAPSHOT",
        autoCompilerPlugins := true,
        addCompilerPlugin("org.scalamock" %% "scalamock-compiler-plugin" % "2.0-SNAPSHOT"))
    
      lazy val myproject = Project("MyProject", file(".")) settings(generateMocksSettings: _*) configs(Mock)
    }

Simple mocking

  1. Now we’ve got a project, we need some code to test. Let’s start with a simple trait representing a turtle. Create src/main/scala/Turtle.scala containing:
    package com.example
    
    trait Turtle {
      def penDown()
      def penUp()
      def forward(distance: Double)
      def turn(angle: Double)
      def getPosition: (Double, Double)
      def getAngle: Double
    }
  2. The turtle API is not very convenient, we have no way to move to a specific position, instead we need to work out how to get from where we are now to where we want to get by calculating angles and distances. Here’s some code that draws a line from a specific point to another by doing exactly that.

    Create src/main/scala/Controller.scala containing:

    package com.example
    
    import scala.math.{atan2, sqrt}
    
    class Controller(turtle: Turtle) {
    
      def drawLine(start: (Double, Double), end: (Double, Double)) {
        moveTo(start)
    
        val initialAngle = turtle.getAngle
        val deltaPos = delta(start, end)
    
        turtle.turn(angle(deltaPos) - initialAngle)
        turtle.penDown
        turtle.forward(distance(deltaPos))
      }
    
      def delta(pos1: (Double, Double), pos2: (Double, Double)) =
        (pos2._1 - pos1._1, pos2._2 - pos1._2)
    
      def distance(delta: (Double, Double)) =
        sqrt(delta._1 * delta._1 + delta._2 * delta._2)
    
      def angle(delta: (Double, Double)) =
        atan2(delta._2, delta._1)
    
      def moveTo(pos: (Double, Double)) {
        val initialPos = turtle.getPosition
        val initialAngle = turtle.getAngle
    
        val deltaPos = delta(initialPos, pos)
    
        turtle.penUp
        turtle.turn(angle(deltaPos) - initialAngle)
        turtle.forward(distance(deltaPos))
      }
    }
  3. In order to create mock turtles, we need to tell ScalaMock to generate the appropriate code by using the @mock annotation. Create src/generate-mocks/scala/GenerateMocks.scala containing:
    package com.example
    
    import org.scalamock.annotation.mock
    
    @mock[Turtle]
    class Dummy
  4. We can now write a test. We’ll create a mock turtle that pretends to start at the origin (0, 0) and verifies that if we draw a line from (1, 1) to (2, 1) it performs the correct sequence of turns and movements.

    Turtle diagram

    Create src/test/scala/ControllerTest.scala containing:

    package com.example
    
    import org.scalatest.FunSuite
    import org.scalamock.scalatest.MockFactory
    import org.scalamock.generated.GeneratedMockFactory
    import scala.math.{Pi, sqrt}
    
    class ControllerTest extends FunSuite with MockFactory with GeneratedMockFactory {
    
      test("draw line") {
        val mockTurtle = mock[Turtle]
        val controller = new Controller(mockTurtle)
    
        inSequence {
          inAnyOrder {
            mockTurtle.expects.penUp
            mockTurtle.expects.getPosition returning (0.0, 0.0)
            mockTurtle.expects.getAngle returning 0.0
          }
          mockTurtle.expects.turn(~(Pi / 4))
          mockTurtle.expects.forward(~sqrt(2.0))
          mockTurtle.expects.getAngle returning Pi / 4
          mockTurtle.expects.turn(~(-Pi / 4))
          mockTurtle.expects.penDown
          mockTurtle.expects.forward(1.0)
        }
    
        controller.drawLine((1.0, 1.0), (2.0, 1.0))
      }
    }

    This should (hopefully!) be self-explanatory, with one possible exception. The tilde (~) operator represents an epsilon match, useful for taking account of rounding errors when dealing with floating-point values.

  5. Generate mocks with generate-mocks and then run the tests with test:
    $ sbt
    > generate-mocks
    [log generatemocks] Creating mock for: trait Turtle
    > test
    [info] ControllerTest:
    [info] - draw line
    [info] Passed: : Total 1, Failed 0, Errors 0, Passed 1, Skipped 0

Getting clever: Constructors and singleton objects

  1. Turtles use ink. Let’s define a singleton object that keeps track of how much we’ve used.

    Create src/main/scala/InkReservoir.scala containing:

    package com.example
    
    object InkReservoir {
    
      def use(r: Double, g: Double, b: Double) {
        red -= r
        green -= g
        blue -= b
      }
    
      private var red = 10.0
      private var green = 10.0
      private var blue = 10.0
    }
  2. And now let’s create a concrete implementation of our Turtle trait, which adds the ability to define a pen colour, together with a factory method implemented in its companion object.

    Create src/main/scala/ColouredTurtle.scala containing:

    package com.example
    
    import scala.math.{cos, sin}
    
    class ColouredTurtle(r: Double, g: Double, b: Double) extends Turtle {
      def penDown() { penIsDown = true }
      def penUp() { penIsDown = false }
      def turn(angle: Double) { theta += angle}
      def getPosition: (Double, Double) = (x, y)
      def getAngle: Double = theta
      def forward(d: Double) {
        x += sin(theta) * d
        y += cos(theta) * d
        if (penIsDown)
          InkReservoir.use(r * d, g * d, b * d)
      }
    
      private var penIsDown = false
      private var x = 0.0
      private var y = 0.0
      private var theta = 0.0
    }
    
    object ColouredTurtle {
    
      def apply(colour: Symbol) = {
        val (r, g, b) = colourMap(colour)
        new ColouredTurtle(r, g, b)
      }
    
      private val colourMap = Map('red -&gt; (1.0, 0.0, 0.0), 'green -&gt; (0.0, 1.0, 0.0), 'blue -&gt; (0.0, 0.0, 1.0))
    }
  3. To mock ColouredTurtle, first we need to add another @mock annotation to GenerateMocks.scala:
    @mock[ColouredTurtle]
  4. We can now write a test to verify that our factory method works.

    Create src/test/scala/ColouredTurtleTest.scala:

    package com.example
    
    import org.scalatest.FunSuite
    import org.scalamock.scalatest.MockFactory
    import org.scalamock.generated.GeneratedMockFactory
    
    class ColouredTurtleTest extends FunSuite with MockFactory with GeneratedMockFactory {
    
      test("coloured turtles") {
        val m1 = mock[ColouredTurtle]
        val m2 = mock[ColouredTurtle]
    
        m1.expects.newInstance(1.0, 0.0, 0.0)
        m2.expects.newInstance(0.0, 1.0, 0.0)
        m2.expects.forward(3.0)
    
        val t1 = ColouredTurtle('red)
        val t2 = ColouredTurtle('green)
        t2.forward(3.0)
      }
    }
  5. Run the tests again (don’t forget to run generate-mocks first) to see:
    [info] ColouredTurtleTest:
    [info] - coloured turtles
    [info] ControllerTest:
    [info] - draw line
    [info] Passed: : Total 2, Failed 0, Errors 0, Passed 2, Skipped 0
  6. Finally, we can add a test to verify that we’re keeping track of ink correctly. Let ScalaMock know that we’ll be mocking InkReservoir by adding a @mockObject annotation:
    @mockObject(InkReservoir)</pre>
    
    And add a test to <code>ColouredTurtleTest.scala</code>:
    
    <pre>  test("ink reservoir") {
        val m = mockObject(InkReservoir)
    
        m.expects.use(0.0, 3.0, 0.0)
    
        val t = ColouredTurtle('green)
        t.penDown
        t.forward(3.0)
      }
  7. [info] ControllerTest:
    [info] - draw line
    [info] ColouredTurtleTest:
    [info] - coloured turtles
    [info] - ink reservoir
    [info] Passed: : Total 3, Failed 0, Errors 0, Passed 3, Skipped 0