scalatestCoreDottyJS/org.scalatest/org.scalatest.prop/TableDrivenPropertyChecks

TableDrivenPropertyChecks

org.scalatest.prop.TableDrivenPropertyChecks

See theTableDrivenPropertyChecks companion object

trait TableDrivenPropertyChecks extends Whenever, Tables

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

This trait contains one exists, forAll, and forEvery method for each TableForN class, TableFor1 through TableFor22, which allow properties to be checked against the rows of a table. It also contains a whenever 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 defines 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.should.Matchers._

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 exists, forAll, and forEvery methods that allow you to check properties using the data provided by a table. Each exists, forAll, and forEvery 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 DiscardedEvaluationException. A DiscardedEvaluationException, 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.

The full list of table methods are:

exists - succeeds if the assertion holds true for at least one element
forAll - succeeds if the assertion holds true for every element
forEvery - same as forAll, but lists all failing elements if it fails (whereas forAll just reports the first failing element) and throws TestFailedException with the first failed check as the cause.

== 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:

`n`	`d`
`Integer.MIN_VALUE`	`Integer.MIN_VALUE`
a valid value	`Integer.MIN_VALUE`
`Integer.MIN_VALUE`	a valid value
`Integer.MIN_VALUE`	zero
a valid value	zero

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]
}

Attributes

Companion: object
Graph
Supertypes: trait Tables

trait Whenever

class Object

trait Matchable

class Any
Known subtypes: trait PropertyChecks

object PropertyChecks.type

object TableDrivenPropertyChecks.type

Members list

Type members

Inherited classlikes

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

For example, you could create a table of 5 rows and 2 colums like this:

import org.scalatest.prop.Tables._

val examples =
 Table(
   ("a", "b"),
   (  1,   2),
   (  2,   4),
   (  4,   8),
   (  8,  16),
   ( 16,  32)
 )

Because you supplied 2 members in each tuple, the type you'll get back will be a TableFor2. If you wanted a table with just one column you could write this:

val moreExamples =
 Table(
   "powerOfTwo",
        1,
        2,
        4,
        8,
        16
 )

Or if you wanted a table with 10 columns and 10 rows, you could do this:

val multiplicationTable =
 Table(
   ("a", "b", "c", "d", "e", "f", "g", "h", "i", "j"),
   (  1,   2,   3,   4,   5,   6,   7,   8,   9,  10),
   (  2,   4,   6,   8,  10,  12,  14,  16,  18,  20),
   (  3,   6,   9,  12,  15,  18,  21,  24,  27,  30),
   (  4,   8,  12,  16,  20,  24,  28,  32,  36,  40),
   (  5,  10,  15,  20,  25,  30,  35,  40,  45,  50),
   (  6,  12,  18,  24,  30,  36,  42,  48,  54,  60),
   (  7,  14,  21,  28,  35,  42,  49,  56,  63,  70),
   (  8,  16,  24,  32,  40,  48,  56,  64,  72,  80),
   (  9,  18,  27,  36,  45,  54,  63,  72,  81,  90),
   ( 10,  20,  30,  40,  50,  60,  70,  80,  90, 100)
 )

The type of multiplicationTable would be TableFor10. You can pass the resulting tables to a forAll method (defined in trait PropertyChecks), to perform a property check with the data in the table. Or, because tables are sequences of tuples, you can treat them as a Seq.

Attributes

Inherited from:: Tables
Supertypes: class Object

trait Matchable

class Any

Value members

Concrete methods

Performs a property check by applying the specified property check function to each row of the specified TableFor1 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor2 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor3 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor4 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor5 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor6 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor7 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor8 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor9 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor10 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor11 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor12 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor13 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor14 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor15 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor16 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor17 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor18 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor19 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor20 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor21 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor22 and succeeding if at least one element satisfies the property check.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

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

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor1 and reporting every error.

The difference between forEvery and forAll is that forEvery will continue to inspect all elements after first failure, and report all failures, whereas forAll will stop on (and only report) the first failure.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor2 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor3 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor4 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor5 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor6 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor7 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor8 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor9 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor10 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor11 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor12 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor13 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor14 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor15 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor16 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor17 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor18 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor19 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor20 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor21 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Performs a property check by applying the specified property check function to each row of the specified TableFor22 and reporting every error.

Value parameters

fun: the property check function to apply to each row of data in the table
table: the table of data with which to perform the property check

Attributes

Inherited methods

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.Matchers._

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 === (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.

Value parameters

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

Attributes

Inherited from:: Whenever

In this article

Generated with