trait
GenPoly extends AnyRef
Type Members
-
abstract
type
T
Abstract Value Members
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abstract
val
genT: Gen[Random with Sized, T]
Concrete Value Members
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final
def
!=(arg0: Any): Boolean
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final
def
##(): Int
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final
def
==(arg0: Any): Boolean
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final
def
asInstanceOf[T0]: T0
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def
clone(): AnyRef
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-
-
def
finalize(): Unit
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final
def
getClass(): Class[_]
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def
hashCode(): Int
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final
def
isInstanceOf[T0]: Boolean
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final
def
notify(): Unit
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final
def
notifyAll(): Unit
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final
def
synchronized[T0](arg0: ⇒ T0): T0
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def
toString(): String
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final
def
wait(): Unit
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final
def
wait(arg0: Long, arg1: Int): Unit
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final
def
wait(arg0: Long): Unit
GenPoly
provides evidence that an instance ofGen[T]
exists for some concrete but unknown typeT
. Subtypes ofGenPoly
provide additional constraints on the type ofT
, such as that an instance ofOrdering[T]
orNumeric[T]
exists. Users can also extendGenPoly
to add their own constraints.This allows construction of polymorphic generators where the the type is known to satisfy certain constraints even though the type itself is unknown.
For instance, consider the following generalized algebraic data type:
We would like to test that for any expression we can fuse two mappings. We want to create instances of
Expr
that reflect the full range of values that anExpr
can take, including multiple layers of nested mappings and mappings between different types.Since we do not need any constraints on the generated types we can simply use
GenPoly
.GenPoly
includes a convenient generator in its companion object,genPoly
, that generates instances of 40 different types including primitive types and various collections.Using it we can define polymorphic generators for expressions:
Finally, we can test our property:
This will generate expressions with multiple levels of nesting and polymorphic mappings between different types, making sure that the types line up for each mapping. This provides a higher level of confidence in properties than testing with a monomorphic value.
Inspired by Erik Osheim's presentation "Galaxy Brain: type-dependence and state-dependence in property-based testing" http://plastic-idolatry.com/erik/oslo2019.pdf.