Supertrait for CheckerAsserting
typeclasses, which are used to implement and determine the result
type of GeneratorDrivenPropertyChecks's apply
and forAll
method.
Trait that contains several “check” methods that perform ScalaCheck property checks.
Trait that contains several “check” methods that perform ScalaCheck property checks. If ScalaCheck finds a test case for which a property doesn't hold, the problem will be reported as a ScalaTest test failure.
To use ScalaCheck, you specify properties and, in some cases, generators that generate test data. You need not always
create generators, because ScalaCheck provides many default generators for you that can be used in many situations.
ScalaCheck will use the generators to generate test data and with that data run tests that check that the property holds.
Property-based tests can, therefore, give you a lot more testing for a lot less code than assertion-based tests.
Here's an example of using ScalaCheck from a JUnitSuite
:
import org.scalatest.junit.JUnitSuite import org.scalatest.prop.Checkers import org.scalacheck.Arbitrary._ import org.scalacheck.Prop._ class MySuite extends JUnitSuite with Checkers { @Test def testConcat() { check((a: List[Int], b: List[Int]) => a.size + b.size == (a ::: b).size) } }
The check
method, defined in Checkers
, makes it easy to write property-based tests inside
ScalaTest, JUnit, and TestNG test suites. This example specifies a property that List
's :::
method
should obey. ScalaCheck properties are expressed as function values that take the required
test data as parameters. ScalaCheck will generate test data using generators and
repeatedly pass generated data to the function. In this case, the test data is composed of integer lists named a
and b
.
Inside the body of the function, you see:
a.size + b.size == (a ::: b).size
The property in this case is a Boolean
expression that will yield true if the size of the concatenated list is equal
to the size of each individual list added together. With this small amount
of code, ScalaCheck will generate possibly hundreds of value pairs for a
and b
and test each pair, looking for
a pair of integers for which the property doesn't hold. If the property holds true for every value ScalaCheck tries,
check
returns normally. Otherwise, check
will complete abruptly with a TestFailedException
that
contains information about the failure, including the values that cause the property to be false.
For more information on using ScalaCheck properties, see the documentation for ScalaCheck, which is available from http://code.google.com/p/scalacheck/.
To execute a suite that mixes in Checkers
with ScalaTest's Runner
, you must include ScalaCheck's jar file on the class path or runpath.
The property checks performed by the check
methods of this trait can be flexibly configured via the services
provided by supertrait Configuration
. The five configuration parameters for property checks along with their
default values and meanings are described in the following table:
Configuration Parameter | Default Value | Meaning |
---|---|---|
minSuccessful | 100 | the minimum number of successful property evaluations required for the property to pass |
maxDiscarded | 500 | the maximum number of discarded property evaluations allowed during a property check |
minSize | 0 | the minimum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists) |
maxSize | 100 | the maximum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists) |
workers | 1 | specifies the number of worker threads to use during property evaluation |
The check
methods of trait Checkers
each take a PropertyCheckConfiguration
object as an implicit parameter. This object provides values for each of the five configuration parameters. Trait Configuration
provides an implicit val
named generatorDrivenConfig
with each configuration parameter set to its default value.
If you want to set one or more configuration parameters to a different value for all property checks in a suite you can override this
val (or hide it, for example, if you are importing the members of the Checkers
companion object rather
than mixing in the trait.) For example, if
you want all parameters at their defaults except for minSize
and maxSize
, you can override
generatorDrivenConfig
, like this:
implicit override val generatorDrivenConfig = PropertyCheckConfiguration(minSize = 10, sizeRange = 10)
Or, if hide it by declaring a variable of the same name in whatever scope you want the changed values to be in effect:
implicit val generatorDrivenConfig = PropertyCheckConfiguration(minSize = 10, sizeRange = 10)
In addition to taking a PropertyCheckConfiguration
object as an implicit parameter, the check
methods of trait
Checkers
also take a variable length argument list of PropertyCheckConfigParam
objects that you can use to override the values provided by the implicit PropertyCheckConfiguration
for a single check
invocation. You place these configuration settings after the property or property function, For example, if you want to
set minSuccessful
to 500 for just one particular check
invocation,
you can do so like this:
check((n: Int) => n + 0 == n, minSuccessful(500))
This invocation of check
will use 500 for minSuccessful
and whatever values are specified by the
implicitly passed PropertyCheckConfiguration
object for the other configuration parameters.
If you want to set multiple configuration parameters in this way, just list them separated by commas:
check((n: Int) => n + 0 == n, minSuccessful(500), maxDiscardedFactor(0.6))
The previous configuration approach works the same in Checkers
as it does in GeneratorDrivenPropertyChecks
.
Trait Checkers
also provides one check
method that takes an org.scalacheck.Test.Parameters
object,
in case you want to configure ScalaCheck that way.
import org.scalacheck.Prop import org.scalacheck.Test.Parameters import org.scalatest.prop.Checkers._ check(Prop.forAll((n: Int) => n + 0 == n), Parameters.Default { override val minSuccessfulTests = 5 })
For more information, see the documentation
for supertrait Configuration
.
Abstract class that in the future will hold an intermediate priority CheckerAsserting
implicit, which will enable inspector expressions
that have result type Expectation
, a more composable form of assertion that returns a result instead of throwing an exception when it fails.
Abstract class that in the future will hold an intermediate priority CheckerAsserting
implicit, which will enable inspector expressions
that have result type Expectation
, a more composable form of assertion that returns a result instead of throwing an exception when it fails.
Trait containing methods that faciliate property checks against generated data.
Trait containing methods that faciliate property checks against generated data.
This trait contains forAll
methods that provide various ways to check properties using
generated data. Use of this trait requires that ScalaCheck be on the class path when you compile and run your tests.
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 ScalaCheckDrivenPropertyChecks
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 }
To test the behavior of Fraction
, you could mix in or import the members of ScalaCheckDrivenPropertyChecks
(and Matchers
) and check a property using a forAll
method, like this:
forAll { (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 ScalaCheckDrivenPropertyChecks
provides overloaded forAll
methods
that allow you to check properties using the data provided by a ScalaCheck generator. The simplest form
of forAll
method takes two parameter lists, the second of which is implicit. The first parameter list
is a "property" function with one to six parameters. An implicit Arbitrary
generator and Shrink
object needs to be supplied for
The forAll
method will pass each row of data to
each parameter type. ScalaCheck provides many implicit Arbitrary
generators for common types such as
Int
, String
, List[Float]
, etc., in its org.scalacheck.Arbitrary
companion
object. So long as you use types for which ScalaCheck already provides implicit Arbitrary
generators, you needn't
worry about them. Same for Shrink
objects, which are provided by ScalaCheck's org.scalacheck.Shrink
companion
object. Most often you can simply pass a property function to forAll
, and the compiler will grab the implicit
values provided by ScalaCheck.
The forAll
methods use the supplied Arbitrary
generators to generate example
arguments and pass them to the property function, and
generate a ScalaCheckDrivenPropertyCheckFailedException
if the function
completes abruptly for any exception that would normally cause a test to
fail in ScalaTest other than DiscardedEvaluationException
. An
DiscardedEvaluationException
,
which is thrown by the whenever
method (defined in trait Whenever
, which this trait extends) to indicate
a condition required by the property function is not met by a row
of passed data, will simply cause forAll
to discard that row of data.
You can optionally specify string names for the arguments passed to a property function, which will be used
in any error message when describing the argument values that caused the failure. To supply the names, place them in a comma separated list
in parentheses after forAll
before the property function (a curried form of forAll
). Here's
an example:
forAll ("a", "b") { (a: String, b: String) => a.length + b.length should equal ((a + b).length + 1) // Should fail }
When this fails, you'll see an error message that includes this:
Occurred when passed generated values ( a = "", b = "" )
When you don't supply argument names, the error message will say arg0
, arg1
, etc..
For example, this property check:
forAll { (a: String, b: String) => a.length + b.length should equal ((a + b).length + 1) // Should fail }
Will fail with an error message that includes:
Occurred when passed generated values ( arg0 = "", arg1 = "" )
ScalaCheck provides a nice library of compositors that makes it easy to create your own custom generators. If you
want to supply custom generators to a property check, place them in parentheses after forAll
, before
the property check function (a curried form of forAll
).
For example, to create a generator of even integers between (and including) -2000 and 2000, you could write this:
import org.scalacheck.Gen val evenInts = for (n <- Gen.choose(-1000, 1000)) yield 2 * n
Given this generator, you could use it on a property check like this:
forAll (evenInts) { (n) => n % 2 should equal (0) }
Custom generators are necessary when you want to pass data types not supported by ScalaCheck's arbitrary generators,
but are also useful when some of the values in the full range for the passed types are not valid. For such values you
would use a whenever
clause. In the Fraction
class shown above, neither the passed numerator or
denominator can be Integer.MIN_VALUE
, and the passed denominator cannot be zero. This shows up in the
whenever
clause like this:
whenever (d != 0 && d != Integer.MIN_VALUE && n != Integer.MIN_VALUE) { ...
You could in addition define generators for the numerator and denominator that only produce valid values, like this:
val validNumers = for (n <- Gen.choose(Integer.MIN_VALUE + 1, Integer.MAX_VALUE)) yield n val validDenoms = for (d <- validNumers if d != 0) yield d
You could then use them in the property check like this:
forAll (validNumers, validDenoms) { (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 } }
Note that even if you use generators that don't produce the invalid values, you still need the
whenever
clause. The reason is that once a property fails, ScalaCheck will try and shrink
the values to the smallest values that still cause the property to fail. During this shrinking process ScalaCheck
may pass invalid values. The whenever
clause is still needed to guard against those values. (The
whenever
clause also clarifies to readers of the code exactly what the property is in a succinct
way, without requiring that they find and understand the generator definitions.)
If you want to supply both generators and named arguments, you can do so by providing a list of (<generator>, <name>)
pairs
in parentheses after forAll
, before the property function. Here's an example:
forAll ((validNumers, "n"), (validDenoms, "d")) { (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 } }
Were this property check to fail, it would mention the names n and d in the error message, like this:
Occurred when passed generated values ( n = 17, d = 21 )
The property checks performed by the forAll
methods of this trait can be flexibly configured via the services
provided by supertrait Configuration
. The five configuration parameters for property checks along with their
default values and meanings are described in the following table:
Configuration Parameter | Default Value | Meaning |
---|---|---|
minSuccessful | 100 | the minimum number of successful property evaluations required for the property to pass |
maxDiscardedFactor | 500 | the maximum discarded factor property evaluations allowed during a property check |
minSize | 0 | the minimum size parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists) |
sizeRange | 100 | the size range parameter to provide to ScalaCheck, which it will use when generating objects for which size matters (such as strings or lists) |
workers | 1 | specifies the number of worker threads to use during property evaluation |
The forAll
methods of trait ScalaCheckDrivenPropertyChecks
each take a PropertyCheckConfiguration
object as an implicit parameter. This object provides values for each of the five configuration parameters. Trait Configuration
provides an implicit val
named generatorDrivenConfig
with each configuration parameter set to its default value.
If you want to set one or more configuration parameters to a different value for all property checks in a suite you can override this
val (or hide it, for example, if you are importing the members of the ScalaCheckDrivenPropertyChecks
companion object rather
than mixing in the trait.) For example, if
you want all parameters at their defaults except for minSize
and sizeRange
, you can override
generatorDrivenConfig
, like this:
implicit override val generatorDrivenConfig = PropertyCheckConfiguration(minSize = 10, sizeRange = 10)
Or, hide it by declaring a variable of the same name in whatever scope you want the changed values to be in effect:
implicit val generatorDrivenConfig = PropertyCheckConfiguration(minSize = 10, sizeRange = 10)
In addition to taking a PropertyCheckConfiguration
object as an implicit parameter, the forAll
methods of trait
ScalaCheckDrivenPropertyChecks
also take a variable length argument list of PropertyCheckConfigParam
objects that you can use to override the values provided by the implicit PropertyCheckConfiguration
for a single forAll
invocation. For example, if you want to set minSuccessful
to 500 for just one particular forAll
invocation,
you can do so like this:
forAll (minSuccessful(500)) { (n: Int, d: Int) => ...
This invocation of forAll
will use 500 for minSuccessful
and whatever values are specified by the
implicitly passed PropertyCheckConfiguration
object for the other configuration parameters.
If you want to set multiple configuration parameters in this way, just list them separated by commas:
forAll (minSuccessful(500), maxDiscardedFactor(0.6)) { (n: Int, d: Int) => ...
If you are using an overloaded form of forAll
that already takes an initial parameter list, just
add the configuration parameters after the list of generators, names, or generator/name pairs, as in:
// If providing argument names forAll ("n", "d", minSuccessful(500), maxDiscardedFactor(0.6)) { (n: Int, d: Int) => ... // If providing generators forAll (validNumers, validDenoms, minSuccessful(500), maxDiscardedFactor(0.6)) { (n: Int, d: Int) => ... // If providing (<generators>, <name>) pairs forAll ((validNumers, "n"), (validDenoms, "d"), minSuccessful(500), maxDiscardedFactor(0.6)) { (n: Int, d: Int) => ...
For more information, see the documentation for supertrait Configuration
.
Trait that facilitates property checks on data supplied by tables and ScalaCheck generators.
Trait that facilitates property checks on data supplied by tables and ScalaCheck generators.
This trait extends both TableDrivenPropertyChecks
and
ScalaCheckDrivenPropertyChecks
. Thus by mixing in
this trait you can perform property checks on data supplied either by tables or generators. For the details of
table- and generator-driven property checks, see the documentation for each by following the links above.
For a quick example of using both table and generator-driven property checks in the same suite of tests, however,
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 }
If you mix in PropertyChecks
, you could use a generator-driven property check to test that the passed values for numerator and
denominator are properly normalized, like this:
forAll { (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 shouldEqual 0 f.denom should be > 0 } }
And you could use a table-driven property check to test that all combinations of invalid values passed to the Fraction
constructor
produce the expected IllegalArgumentException
, like this:
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) ) forAll (invalidCombos) { (n: Int, d: Int) => an [IllegalArgumentException] should be thrownBy { new Fraction(n, d) } }
Class holding lowest priority CheckerAsserting
implicit, which enables GeneratorDrivenPropertyChecks expressions that have result type Unit
.
Class holding lowest priority CheckerAsserting
implicit, which enables GeneratorDrivenPropertyChecks expressions that have result type Unit
.
Companion object to CheckerAsserting
that provides two implicit providers, a higher priority one for passed functions that have result
type Assertion
, which also yields result type Assertion
, and one for any other type, which yields result type Unit
.
Companion object to CheckerAsserting
that provides two implicit providers, a higher priority one for passed functions that have result
type Assertion
, which also yields result type Assertion
, and one for any other type, which yields result type Unit
.
Companion object that facilitates the importing of Checkers
members as
an alternative to mixing it in.
Companion object that facilitates the importing of Checkers
members as
an alternative to mixing it in. One use case is to import Checkers
members so you can use
them in the Scala interpreter.
Companion object that facilitates the importing of PropertyChecks
members as
an alternative to mixing it in.
Companion object that facilitates the importing of PropertyChecks
members as
an alternative to mixing it in. One use case is to import PropertyChecks
members so you can use
them in the Scala interpreter.
Supertrait for
CheckerAsserting
typeclasses, which are used to implement and determine the result type of GeneratorDrivenPropertyChecks'sapply
andforAll
method.Currently, an GeneratorDrivenPropertyChecks expression will have result type
Assertion
, if the function passed has result typeAssertion
, else it will have result typeUnit
.