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.
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)
}
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)
}
Object containing one apply factory method for each TableFor<n> class.
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
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.
the table of data with which to perform the property check
the property check function to apply to each row of data in the table
Evaluates the passed code block if the passed boolean condition is true, else throws UnmetConditionException.
Evaluates the passed code block if the passed boolean condition is true, else throws UnmetConditionException.
The whenever method can be used inside property check functions to skip 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 skip 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 UnmetConditionException,
which will cause the forAll method to skip that row.
the boolean condition that determines whether whenever will evaluate the
fun function (condition is true) or throws UnmetConditionException (<code>condition<code> is false)
funthe function to evaluate if the specified condition is true
definition classes: Whenever
Inherited from Tables
Inherited from Whenever
Inherited from AnyRef
Inherited from Any
Trait containing methods that faciliate property checks against tables of data.
This trait contains one
forAllmethod for eachTableForNclass,TableFor1throughTableFor22, which allow properties to be checked against the rows of a table. It also contains awherevermethod that can be used to indicate a property need only hold whenever some condition is true.For an example of trait
TableDrivenPropertyChecksin action, imagine you want to test thisFractionclass: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 }
TableDrivenPropertyChecksallows 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 objectTable. 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 twoInts, all subsequent tuples must contain twoInt(i.e., have typeTuple2[Int, Int]).To test the behavior of
Fraction, you could create a table of numerators and denominators to pass to the constructor of theFractionclass using one of theapplyfactory methods declared inTable, like this:You could then check a property against each row of the table using a
forAllmethod, like this:Trait
TableDrivenPropertyChecksprovides 22 overloadedforAllmethods that allow you to check properties using the data provided by a table. EachforAllmethod 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 toforAlleach contain anInt, aString, and aList[Char], then the function supplied toforAllmust take 3 parameters, anInt, aString, and aList[Char]. TheforAllmethod will pass each row of data to the function, and generate aTableDrivenPropertyCheckFailedExceptionif the function completes abruptly for any row of data with any exception that would normally cause a test to fail in ScalaTest other thanUnmetConditionException. AnUnmetConditionException, which is thrown by thewhenevermethod (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 causeforAllto 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
FiboGenwhosenextmethod returned the next fibonacci number, where next means the next number in the series following the number previously returned bynext. So the first timenextwas called, it would return 0. The next time it was called it would return 1. Then 1. Then 2. Then 3, and so on.FiboGenwould need to maintain state, because it has to remember where it is in the series. In such a situation, you could create aTableFor1(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
forAllsimply 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
Counterclass:class Counter { private var c = 0 def reset() { c = 0 } def click() { c += 1 } def enter(n: Int) { c = n } def count = c }A
Counterkeeps track of how many times itsclickmethod is called. The count starts out at zero and increments with eachclickinvocation. You can also set the count to a specific value by callingenterand passing the value in. And theresetmethod 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 ActionGiven 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) }