org.scalatest.prop

TableDrivenPropertyChecks

trait TableDrivenPropertyChecks extends Whenever with Tables

Trait containing methods that faciliate property checks against tables of data.

This trait contains one forAll method for each TableForN class, TableFor1 through TableFor22, which allow properties to be checked against the rows of a table. It also contains a wherever method that can be used to indicate a property need only hold whenever some condition is true.

For an example of trait TableDrivenPropertyChecks in action, imagine you want to test this Fraction class:

class Fraction(n: Int, d: Int) {

  require(d != 0)
  require(d != Integer.MIN_VALUE)
  require(n != Integer.MIN_VALUE)

  val numer = if (d < 0) -1 * n else n
  val denom = d.abs

  override def toString = numer + " / " + denom
}

TableDrivenPropertyChecks allows you to create tables with between 1 and 22 columns and any number of rows. You create a table by passing tuples to one of the factory methods of object Table. Each tuple must have the same arity (number of members). The first tuple you pass must all be strings, because it define names for the columns. Subsequent tuples define the data. After the initial tuple that contains string column names, all tuples must have the same type. For example, if the first tuple after the column names contains two Ints, all subsequent tuples must contain two Int (i.e., have type Tuple2[Int, Int]).

To test the behavior of Fraction, you could create a table of numerators and denominators to pass to the constructor of the Fraction class using one of the apply factory methods declared in Table, like this:

import org.scalatest.prop.TableDrivenPropertyChecks._

val fractions =
  Table(
    ("n", "d"),  // First tuple defines column names
    (  1,   2),  // Subsequent tuples define the data
    ( -1,   2),
    (  1,  -2),
    ( -1,  -2),
    (  3,   1),
    ( -3,   1),
    ( -3,   0),
    (  3,  -1),
    (  3,  Integer.MIN_VALUE),
    (Integer.MIN_VALUE, 3),
    ( -3,  -1)
  )

You could then check a property against each row of the table using a forAll method, like this:

import org.scalatest.matchers.ShouldMatchers._

forAll (fractions) { (n: Int, d: Int) =>

  whenever (d != 0 && d != Integer.MIN_VALUE
      && n != Integer.MIN_VALUE) {

    val f = new Fraction(n, d)

    if (n < 0 && d < 0 || n > 0 && d > 0)
      f.numer should be > 0
    else if (n != 0)
      f.numer should be < 0
    else
      f.numer should be === 0

    f.denom should be > 0
  }
}

Trait TableDrivenPropertyChecks provides 22 overloaded forAll methods that allow you to check properties using the data provided by a table. Each forAll method takes two parameter lists. The first parameter list is a table. The second parameter list is a function whose argument types and number matches that of the tuples in the table. For example, if the tuples in the table supplied to forAll each contain an Int, a String, and a List[Char], then the function supplied to forAll must take 3 parameters, an Int, a String, and a List[Char]. The forAll method will pass each row of data to the function, and generate a TableDrivenPropertyCheckFailedException if the function completes abruptly for any row of data with any exception that would normally cause a test to fail in ScalaTest other than UnmetConditionException. An UnmetConditionException, which is thrown by the whenever method (also defined in this trait) to indicate a condition required by the property function is not met by a row of passed data, will simply cause forAll to skip that row of data.

Testing stateful functions

One way to use a table with one column is to test subsequent return values of a stateful function. Imagine, for example, you had an object named FiboGen whose next method returned the next fibonacci number, where next means the next number in the series following the number previously returned by next. So the first time next was called, it would return 0. The next time it was called it would return 1. Then 1. Then 2. Then 3, and so on. FiboGen would need to maintain state, because it has to remember where it is in the series. In such a situation, you could create a TableFor1 (a table with one column, which you could alternatively think of as one row), in which each row represents the next value you expect.

val first14FiboNums =
  Table("n", 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233)

Then in your forAll simply call the function and compare it with the expected return value, like this:

 forAll (first14FiboNums) { n =>
   FiboGen.next should equal (n)
 }

Testing mutable objects

If you need to test a mutable object, one way you can use tables is to specify state transitions in a table. For example, imagine you wanted to test this mutable Counter class:

      class Counter {
        private var c = 0
        def reset() { c = 0 }
        def click() { c += 1 }
        def enter(n: Int) { c = n }
        def count = c
      }

A Counter keeps track of how many times its click method is called. The count starts out at zero and increments with each click invocation. You can also set the count to a specific value by calling enter and passing the value in. And the reset method returns the count back to zero. You could define the actions that initiate state transitions with case classes, like this:

      abstract class Action
      case object Start extends Action
      case object Click extends Action
      case class Enter(n: Int) extends Action

Given these actions, you could define a state-transition table like this:

      val stateTransitions =
        Table(
          ("action", "expectedCount"),
          (Start,    0),
          (Click,    1),
          (Click,    2),
          (Click,    3),
          (Enter(5), 5),
          (Click,    6),
          (Enter(1), 1),
          (Click,    2),
          (Click,    3)
        )

To use this in a test, simply do a pattern match inside the function you pass to forAll. Make a pattern for each action, and have the body perform that action when there's a match. Then check that the actual value equals the expected value:

      val counter = new Counter
      forAll (stateTransitions) { (action, expectedCount) =>
        action match {
          case Start => counter.reset()
          case Click => counter.click()
          case Enter(n) => counter.enter(n)
        }
        counter.count should equal (expectedCount)
      }

Testing invalid argument combinations

A table-driven property check can also be helpful to ensure that the proper exception is thrown when invalid data is passed to a method or constructor. For example, the Fraction constructor shown above should throw IllegalArgumentException if Integer.MIN_VALUE is passed for either the numerator or denominator, or zero is passed for the denominator. This yields the following five combinations of invalid data:

nd
Integer.MIN_VALUEInteger.MIN_VALUE
a valid valueInteger.MIN_VALUE
Integer.MIN_VALUEa valid value
Integer.MIN_VALUEzero
a valid valuezero

You can express these combinations in a table:

val invalidCombos =
  Table(
    ("n",               "d"),
    (Integer.MIN_VALUE, Integer.MIN_VALUE),
    (1,                 Integer.MIN_VALUE),
    (Integer.MIN_VALUE, 1),
    (Integer.MIN_VALUE, 0),
    (1,                 0)
  )

Given this table, you could check that all invalid combinations produce IllegalArgumentException, like this:

forAll (invalidCombos) { (n: Int, d: Int) =>
  evaluating {
    new Fraction(n, d)
  } should produce [IllegalArgumentException]
}

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  1. def != (arg0: AnyRef): Boolean

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  3. def ## (): Int

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  5. def == (arg0: Any): Boolean

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  6. object Table extends AnyRef

    Object containing one apply factory method for each TableFor<n> class.

  7. def asInstanceOf [T0] : T0

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  8. def clone (): AnyRef

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  11. def finalize (): Unit

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  12. def forAll [A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V] (table: TableFor22[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor22.

    Performs a property check by applying the specified property check function to each row of the specified TableFor22.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  13. def forAll [A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U] (table: TableFor21[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor21.

    Performs a property check by applying the specified property check function to each row of the specified TableFor21.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  14. def forAll [A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T] (table: TableFor20[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor20.

    Performs a property check by applying the specified property check function to each row of the specified TableFor20.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  15. def forAll [A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S] (table: TableFor19[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor19.

    Performs a property check by applying the specified property check function to each row of the specified TableFor19.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  16. def forAll [A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R] (table: TableFor18[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor18.

    Performs a property check by applying the specified property check function to each row of the specified TableFor18.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  17. def forAll [A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q] (table: TableFor17[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor17.

    Performs a property check by applying the specified property check function to each row of the specified TableFor17.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  18. def forAll [A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P] (table: TableFor16[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor16.

    Performs a property check by applying the specified property check function to each row of the specified TableFor16.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  19. def forAll [A, B, C, D, E, F, G, H, I, J, K, L, M, N, O] (table: TableFor15[A, B, C, D, E, F, G, H, I, J, K, L, M, N, O])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor15.

    Performs a property check by applying the specified property check function to each row of the specified TableFor15.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  20. def forAll [A, B, C, D, E, F, G, H, I, J, K, L, M, N] (table: TableFor14[A, B, C, D, E, F, G, H, I, J, K, L, M, N])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M, N) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor14.

    Performs a property check by applying the specified property check function to each row of the specified TableFor14.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  21. def forAll [A, B, C, D, E, F, G, H, I, J, K, L, M] (table: TableFor13[A, B, C, D, E, F, G, H, I, J, K, L, M])(fun: (A, B, C, D, E, F, G, H, I, J, K, L, M) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor13.

    Performs a property check by applying the specified property check function to each row of the specified TableFor13.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  22. def forAll [A, B, C, D, E, F, G, H, I, J, K, L] (table: TableFor12[A, B, C, D, E, F, G, H, I, J, K, L])(fun: (A, B, C, D, E, F, G, H, I, J, K, L) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor12.

    Performs a property check by applying the specified property check function to each row of the specified TableFor12.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  23. def forAll [A, B, C, D, E, F, G, H, I, J, K] (table: TableFor11[A, B, C, D, E, F, G, H, I, J, K])(fun: (A, B, C, D, E, F, G, H, I, J, K) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor11.

    Performs a property check by applying the specified property check function to each row of the specified TableFor11.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  24. def forAll [A, B, C, D, E, F, G, H, I, J] (table: TableFor10[A, B, C, D, E, F, G, H, I, J])(fun: (A, B, C, D, E, F, G, H, I, J) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor10.

    Performs a property check by applying the specified property check function to each row of the specified TableFor10.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  25. def forAll [A, B, C, D, E, F, G, H, I] (table: TableFor9[A, B, C, D, E, F, G, H, I])(fun: (A, B, C, D, E, F, G, H, I) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor9.

    Performs a property check by applying the specified property check function to each row of the specified TableFor9.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  26. def forAll [A, B, C, D, E, F, G, H] (table: TableFor8[A, B, C, D, E, F, G, H])(fun: (A, B, C, D, E, F, G, H) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor8.

    Performs a property check by applying the specified property check function to each row of the specified TableFor8.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  27. def forAll [A, B, C, D, E, F, G] (table: TableFor7[A, B, C, D, E, F, G])(fun: (A, B, C, D, E, F, G) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor7.

    Performs a property check by applying the specified property check function to each row of the specified TableFor7.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  28. def forAll [A, B, C, D, E, F] (table: TableFor6[A, B, C, D, E, F])(fun: (A, B, C, D, E, F) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor6.

    Performs a property check by applying the specified property check function to each row of the specified TableFor6.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  29. def forAll [A, B, C, D, E] (table: TableFor5[A, B, C, D, E])(fun: (A, B, C, D, E) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor5.

    Performs a property check by applying the specified property check function to each row of the specified TableFor5.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  30. def forAll [A, B, C, D] (table: TableFor4[A, B, C, D])(fun: (A, B, C, D) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor4.

    Performs a property check by applying the specified property check function to each row of the specified TableFor4.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  31. def forAll [A, B, C] (table: TableFor3[A, B, C])(fun: (A, B, C) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor3.

    Performs a property check by applying the specified property check function to each row of the specified TableFor3.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  32. def forAll [A, B] (table: TableFor2[A, B])(fun: (A, B) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor2.

    Performs a property check by applying the specified property check function to each row of the specified TableFor2.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  33. def forAll [A] (table: TableFor1[A])(fun: (A) ⇒ Unit): Unit

    Performs a property check by applying the specified property check function to each row of the specified TableFor1.

    Performs a property check by applying the specified property check function to each row of the specified TableFor1.

    table

    the table of data with which to perform the property check

    fun

    the property check function to apply to each row of data in the table

  34. def getClass (): java.lang.Class[_]

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  36. def isInstanceOf [T0] : Boolean

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  37. def ne (arg0: AnyRef): Boolean

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  38. def notify (): Unit

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  39. def notifyAll (): Unit

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  40. def synchronized [T0] (arg0: ⇒ T0): T0

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  41. def toString (): String

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  42. def wait (): Unit

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  43. def wait (arg0: Long, arg1: Int): Unit

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  44. def wait (arg0: Long): Unit

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  45. def whenever (condition: Boolean)(fun: ⇒ Unit): Unit

    Evaluates the passed code block if the passed boolean condition is true, else throws DiscardedEvaluationException.

    Evaluates the passed code block if the passed boolean condition is true, else throws DiscardedEvaluationException.

    The whenever method can be used inside property check functions to discard invocations of the function with data for which it is known the property would fail. For example, given the following Fraction class:

    class Fraction(n: Int, d: Int) {
    
      require(d != 0)
      require(d != Integer.MIN_VALUE)
      require(n != Integer.MIN_VALUE)
    
      val numer = if (d < 0) -1 * n else n
      val denom = d.abs
    
      override def toString = numer + " / " + denom
    }
    

    import org.scalatest.prop.TableDrivenPropertyChecks._
    
    val fractions =
      Table(
        ("n", "d"),
        (  1,   2),
        ( -1,   2),
        (  1,  -2),
        ( -1,  -2),
        (  3,   1),
        ( -3,   1),
        ( -3,   0),
        (  3,  -1),
        (  3,  Integer.MIN_VALUE),
        (Integer.MIN_VALUE, 3),
        ( -3,  -1)
      )
    

    Imagine you wanted to check a property against this class with data that includes some value that are rejected by the constructor, such as a denominator of zero, which should result in an IllegalArgumentException. You could use whenever to discard any rows in the fraction that represent illegal arguments, like this:

    import org.scalatest.matchers.ShouldMatchers._
    
    forAll (fractions) { (n: Int, d: Int) =>
    
      whenever (d != 0 && d != Integer.MIN_VALUE
          && n != Integer.MIN_VALUE) {
    
        val f = new Fraction(n, d)
    
        if (n < 0 && d < 0 || n > 0 && d > 0)
          f.numer should be > 0
        else if (n != 0)
          f.numer should be < 0
        else
          f.numer should be === 0
    
        f.denom should be > 0
      }
    }
    

    In this example, rows 6, 8, and 9 have values that would cause a false to be passed to whenever. (For example, in row 6, d is 0, which means d != 0 will be false.) For those rows, whenever will throw DiscardedEvaluationException, which will cause the forAll method to discard that row.

    condition

    the boolean condition that determines whether whenever will evaluate the fun function (condition is true) or throws DiscardedEvaluationException (condition is false)

    fun

    the function to evaluate if the specified condition is true

    Definition Classes
    Whenever

Inherited from Tables

Inherited from Whenever

Inherited from AnyRef

Inherited from Any