There are many great testing libraries in Scala. But most of them target experienced programmers. In contrast, hwtest is intended for more inexperienced programmers, especially in the context of a course where

• a teacher/instructor/TA creates the problems and provides test cases (in a lightweight format), and
• a student solves the problems and runs their code against the provided test cases to check their work. If desired, the teacher could also run the student code against a more extensive set of tests for grading purposes.

Of course, this is not a new idea, with variations going back decades and with many tutorial websites working in a similar fashion. hwtest implements this system for Scala and lets you create your own custom problems.

If you use sbt, add these lines to your build.sbt file.

  libraryDependencies += "org.scalatest" %% "scalatest" % "3.2.12"
  libraryDependencies += "org.okasaki" %% "hwtest" % "1.0.0"

• Guide for Teachers
• Guide for Students
• API

A teacher might distribute the following starter code (most likely with more explanation elsewhere for what the functions are supposed to accomplish):

object hwExample extends hwtest.hw("CS123"):
  def userName = ???

  def square(x: Int): Int = ???
  test("square", square, "x")

  def isOdd(n: Int): Boolean = ???
  ignoretest("isOdd", isOdd, "n")

The first thing the student should do is fill in their userName:

  def userName = "Margaret Hamilton"

Then they fill in the body of the first problem:

  def square(x: Int): Int = x*x

At this point, they run their program to check their first answer, receiving this report:

Margaret Hamilton
Data source: hwExample.tests (remote)
Begin testing square at Tue Aug 09 10:12:48 EDT 2022
.....
Passed 5/5 tests in 1.21 seconds.
***** Ignoring tests for isOdd.

Good, the first function passes the test cases! Each . indicates a passed test case. Now they work on the second problem:

  def isOdd(n: Int): Boolean =
    if n%2 == 1 then true else false

But re-running the tests doesn't display the results for the second function? Oh, they realize they forgot to change the ignoretest to test! A quick edit and re-running the tests displays

CS123: hwExample (hwtest 1.0.0)
Margaret Hamilton
Data source: hwExample.tests (remote)
Begin testing square at Tue Aug 09 10:15:22 EDT 2022
.....
Passed 5/5 tests in 0.74 seconds.
Begin testing isOdd at Tue Aug 09 10:15:23 EDT 2022
....
Test #5 *** FAILED ***
  n = -21
  Expected answer: true
  Received answer: false
Passed 4/5 tests in 0.09 seconds.

Uh oh. isOdd failed for n = -21. What's going on? Hmm. Trying that example in a REPL, they eventually realize that -21 % 2 is -1 not 1, and fix their code to

  def isOdd(n: Int): Boolean =
    if n%2 != 0 then true else false

Running their code again produces

CS123: hwExample (hwtest 1.0.0)
Margaret Hamilton
Data source: hwExample.tests (remote)
Begin testing square at Tue Aug 09 10:24:25 EDT 2022
.....
Passed 5/5 tests in 0.69 seconds.
Begin testing isOdd at Tue Aug 09 10:24:25 EDT 2022
.....
Passed 5/5 tests in 0.15 seconds.

Victory!