Generating Enums
The syntax sugar for defining strategies for enum
s is currently somewhat
limited. Creating such strategies with prop_compose!
is possible but
generally is not very readable, so in most cases defining the function by
hand is preferable.
The core building block is the
prop_oneof!
macro, in which you list one case for each case in your enum
. For enum
s
which have no data, the strategy for each case is
Just(YourEnum::TheCase)
. Enum cases with data generally require putting
the data in a tuple and then using prop_map
to map it into the enum case.
Here is a simple example:
#![allow(unused)] fn main() { extern crate proptest; use proptest::prelude::*; #[derive(Debug, Clone)] enum MyEnum { SimpleCase, CaseWithSingleDatum(u32), CaseWithMultipleData(u32, String), } fn my_enum_strategy() -> impl Strategy<Value = MyEnum> { prop_oneof![ // For cases without data, `Just` is all you need Just(MyEnum::SimpleCase), // For cases with data, write a strategy for the interior data, then // map into the actual enum case. any::<u32>().prop_map(MyEnum::CaseWithSingleDatum), (any::<u32>(), ".*").prop_map( |(a, b)| MyEnum::CaseWithMultipleData(a, b)), ] } }
In general, it is best to list the enum cases in order from “simplest” to “most complex”, since shrinking will shrink down toward items earlier in the list.
For particularly complex enum cases, it can be helpful to extract the strategy
for that case to a separate strategy. Here,
prop_compose!
can be of use.
#![allow(unused)] fn main() { extern crate proptest; use proptest::prelude::*; #[derive(Debug, Clone)] enum MyComplexEnum { SimpleCase, AnotherSimpleCase, ComplexCase { product_code: String, id: u64, chapter: String, }, } prop_compose! { fn my_complex_enum_complex_case()( product_code in "[0-9A-Z]{10,20}", id in 1u64..10000u64, chapter in "X{0,2}(V?I{1,3}|IV|IX)", ) -> MyComplexEnum { MyComplexEnum::ComplexCase { product_code, id, chapter } } } fn my_enum_strategy() -> BoxedStrategy<MyComplexEnum> { prop_oneof![ Just(MyComplexEnum::SimpleCase), Just(MyComplexEnum::AnotherSimpleCase), my_complex_enum_complex_case(), ].boxed() } }