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 Int
s, 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) }
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 an 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] }
o != arg0
is the same as !(o == (arg0))
.
o != arg0
is the same as !(o == (arg0))
.
the object to compare against this object for dis-equality.
false
if the receiver object is equivalent to the argument; true
otherwise.
o == arg0
is the same as if (o eq null) arg0 eq null else o.equals(arg0)
.
o == arg0
is the same as if (o eq null) arg0 eq null else o.equals(arg0)
.
the object to compare against this object for equality.
true
if the receiver object is equivalent to the argument; false
otherwise.
o == arg0
is the same as o.equals(arg0)
.
o == arg0
is the same as o.equals(arg0)
.
the object to compare against this object for equality.
true
if the receiver object is equivalent to the argument; false
otherwise.
Object containing one apply
factory method for each TableFor<n>
class.
This method is used to cast the receiver object to be of type T0
.
This method is used to cast the receiver object to be of type T0
.
Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression
1.asInstanceOf[String]
will throw a ClassCastException
at runtime, while the expression
List(1).asInstanceOf[List[String]]
will not. In the latter example, because the type argument is erased as
part of compilation it is not possible to check whether the contents of the list are of the requested typed.
the receiver object.
This method creates and returns a copy of the receiver object.
This method creates and returns a copy of the receiver object.
The default implementation of the clone
method is platform dependent.
a copy of the receiver object.
This method is used to test whether the argument (arg0
) is a reference to the
receiver object (this
).
This method is used to test whether the argument (arg0
) is a reference to the
receiver object (this
).
The eq
method implements an [http://en.wikipedia.org/wiki/Equivalence_relation equivalence relation] on
non-null instances of AnyRef
:
* It is reflexive: for any non-null instance x
of type AnyRef
, x.eq(x)
returns true
.
* It is symmetric: for any non-null instances x
and y
of type AnyRef
, x.eq(y)
returns true
if and
only if y.eq(x)
returns true
.
* It is transitive: for any non-null instances x
, y
, and z
of type AnyRef
if x.eq(y)
returns true
and y.eq(z)
returns true
, then x.eq(z)
returns true
.
Additionally, the eq
method has three other properties.
* It is consistent: for any non-null instances x
and y
of type AnyRef
, multiple invocations of
x.eq(y)
consistently returns true
or consistently returns false
.
* For any non-null instance x
of type AnyRef
, x.eq(null)
and null.eq(x)
returns false
.
* null.eq(null)
returns true
.
When overriding the equals
or hashCode
methods, it is important to ensure that their behavior is
consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2
), they
should be equal to each other (o1 == o2
) and they should hash to the same value (o1.hashCode == o2.hashCode
).
the object to compare against this object for reference equality.
true
if the argument is a reference to the receiver object; false
otherwise.
This method is used to compare the receiver object (this
) with the argument object (arg0
) for equivalence.
This method is used to compare the receiver object (this
) with the argument object (arg0
) for equivalence.
The default implementations of this method is an [http://en.wikipedia.org/wiki/Equivalence_relation equivalence
relation]:
* It is reflexive: for any instance x
of type Any
, x.equals(x)
should return true
.
* It is symmetric: for any instances x
and y
of type Any
, x.equals(y)
should return true
if and
only if y.equals(x)
returns true
.
* It is transitive: for any instances x
, y
, and z
of type AnyRef
if x.equals(y)
returns true
and
y.equals(z)
returns true
, then x.equals(z)
should return true
.
If you override this method, you should verify that your implementation remains an equivalence relation.
Additionally, when overriding this method it is often necessary to override hashCode
to ensure that objects
that are "equal" (o1.equals(o2)
returns true
) hash to the same scala.Int
(o1.hashCode.equals(o2.hashCode)
).
the object to compare against this object for equality.
true
if the receiver object is equivalent to the argument; false
otherwise.
This method is called by the garbage collector on the receiver object when garbage collection determines that there are no more references to the object.
This method is called by the garbage collector on the receiver object when garbage collection determines that there are no more references to the object.
The details of when and if the finalize
method are invoked, as well as the interaction between finalize
and non-local returns and exceptions, are all platform dependent.
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
Returns a representation that corresponds to the dynamic class of the receiver object.
Returns a representation that corresponds to the dynamic class of the receiver object.
The nature of the representation is platform dependent.
a representation that corresponds to the dynamic class of the receiver object.
Returns a hash code value for the object.
Returns a hash code value for the object.
The default hashing algorithm is platform dependent.
Note that it is allowed for two objects to have identical hash codes (o1.hashCode.equals(o2.hashCode)
) yet
not be equal (o1.equals(o2)
returns false
). A degenerate implementation could always return 0
.
However, it is required that if two objects are equal (o1.equals(o2)
returns true
) that they have
identical hash codes (o1.hashCode.equals(o2.hashCode)
). Therefore, when overriding this method, be sure
to verify that the behavior is consistent with the equals
method.
the hash code value for the object.
This method is used to test whether the dynamic type of the receiver object is T0
.
This method is used to test whether the dynamic type of the receiver object is T0
.
Note that the test result of the test is modulo Scala's erasure semantics. Therefore the expression
1.isInstanceOf[String]
will return false
, while the expression List(1).isInstanceOf[List[String]]
will
return true
. In the latter example, because the type argument is erased as part of compilation it is not
possible to check whether the contents of the list are of the requested typed.
true
if the receiver object is an instance of erasure of type T0
; false
otherwise.
o.ne(arg0)
is the same as !(o.eq(arg0))
.
o.ne(arg0)
is the same as !(o.eq(arg0))
.
the object to compare against this object for reference dis-equality.
false
if the argument is not a reference to the receiver object; true
otherwise.
Wakes up a single thread that is waiting on the receiver object's monitor.
Wakes up a single thread that is waiting on the receiver object's monitor.
Wakes up all threads that are waiting on the receiver object's monitor.
Wakes up all threads that are waiting on the receiver object's monitor.
Returns a string representation of the object.
Returns a string representation of the object.
The default representation is platform dependent.
a string representation of the object.
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 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 UnmetConditionException
,
which will cause the forAll
method to discard 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)
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
Trait containing methods that faciliate property checks against tables of data.
This trait contains one
forAll
method for eachTableForN
class,TableFor1
throughTableFor22
, which allow properties to be checked against the rows of a table. It also contains awherever
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 thisFraction
class: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 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 twoInt
s, 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 theFraction
class using one of theapply
factory methods declared inTable
, like this:You could then check a property against each row of the table using a
forAll
method, like this:Trait
TableDrivenPropertyChecks
provides 22 overloadedforAll
methods that allow you to check properties using the data provided by a table. EachforAll
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 toforAll
each contain anInt
, aString
, and aList[Char]
, then the function supplied toforAll
must take 3 parameters, anInt
, aString
, and aList[Char]
. TheforAll
method will pass each row of data to the function, and generate aTableDrivenPropertyCheckFailedException
if 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 thewhenever
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 causeforAll
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
whosenext
method returned the next fibonacci number, where next means the next number in the series following the number previously returned bynext
. So the first timenext
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 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.Then in your
forAll
simply call the function and compare it with the expected return value, like this: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:A
Counter
keeps track of how many times itsclick
method is called. The count starts out at zero and increments with eachclick
invocation. You can also set the count to a specific value by callingenter
and passing the value in. And thereset
method returns the count back to zero. You could define the actions that initiate state transitions with case classes, like this:Given these actions, you could define a state-transition table like this:
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: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 throwIllegalArgumentException
ifInteger.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
Integer.MIN_VALUE
Integer.MIN_VALUE
Integer.MIN_VALUE
You an express these combinations in a table:
Given this table, you could check that all invalid combinations produce
IllegalArgumentException
, like this: