Writing BDD style tests with ScalaTest and SBT

In the previous lesson I showed how to write Test-Driven Development (TDD) tests with ScalaTest. ScalaTest also supports a Behavior-Driven Development (BDD) style of testing, which I’ll demonstrate next.

This lesson uses the same SBT project as the previous lesson, so you don’t have to go through the initial setup work again

Creating a Scala class to test

First, create a new Scala class to test. In the src/main/scala/simpletest, create a new file named MathUtils.scala with these contents:

package simpletest

object MathUtils {

    def double(i: Int) = i * 2

}

The BDD tests you’ll write next will test the double method in that class.

Creating ScalaTest BDD-style tests

Next, create a file named MathUtilsTests.scala in the src/test/scala/simpletest directory, and put these contents in that file:

package simpletest

import org.scalatest.FunSpec

class MathUtilsSpec extends FunSpec {

    describe("MathUtils::double") {

        it("should handle 0 as input") {
            val result = MathUtils.double(0)
            assert(result == 0)
        }

        it("should handle 1") {
            val result = MathUtils.double(1)
            assert(result == 2)
        }

        it("should handle really large integers") (pending)

    }

}

As you can see, this is a very different-looking style than the TDD tests in the previous lesson. If you’ve never used a BDD style of testing before, a main idea is that the tests should be relatively easy to read for one of the “domain experts” who work with the programmers to create the application. A few notes about this code:

  • This code uses the FunSpec class where the TDD tests used FunSuite
  • A set of tests begins with describe
  • Each test begins with it. The idea is that the test should read like, “It should do XYZ...,” where “it” is the double function
  • In this example I also showed how to mark a test as “pending”

Running the tests

With those files in place you can again run sbt test. The important part of the output looks like this:

> sbt test

[info] HelloTests:
[info] - the name is set correctly in constructor
[info] - a Person's name can be changed
[info] MathUtilsSpec:
[info] MathUtils::double
[info] - should handle 0 as input
[info] - should handle 1
[info] - should handle really large integers (pending)
[info] Total number of tests run: 4
[info] Suites: completed 2, aborted 0
[info] Tests: succeeded 4, failed 0, canceled 0, ignored 0, pending 1
[info] All tests passed.
[success] Total time: 4 s, completed Jan 6, 2018 4:58:23 PM

A few notes about that output:

  • sbt test ran the previous HelloTests as well as the new MathUtilsSpec tests
  • The pending test shows up in the output and is marked “(pending)”
  • All of the tests passed

If you want to have a little fun with this, change one or more of the tests so they intentionally fail, and then see what the output looks like.

Where to go from here

For more information about SBT and ScalaTest, see the following resources:

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