KotlinFixture

A tool to generate well-defined, but essentially random, input following the idea of constrained non-determinism.

Contents

• Getting started
• Configuration options
• Kotest integration: property based testing
• Java Faker integration: pretty data
• Generex integration: regex to random string
• Related projects
• Contributing
• License

Getting started

Include the following dependency in your build.gradle.kts file:

build.gradle.kts

testImplementation("com.appmattus.fixture:fixture:<latest-version>")

Simply create a fixture and invoke it with the type to be generated:

val fixture = kotlinFixture()

// Generate a list of strings
val aListOfStrings = fixture<List<String>>()

// Nulls are supported
val sometimesNull = fixture<Int?>()

// Create instances of classes
// Optional parameters will be randomly used or overridden
data class ADataClass(val value: String = "default")
val aClass = fixture<ADataClass>()

// Abstract classes will pick a sub-class at random
// This could be a Byte, Double, Long, Float, Int or Short
val anyNumber = fixture<Number>()

// Pick randomly from a list
val randomStringFromTheList = fixture(listOf("Cat", "Dog", "Horse"))
val anotherRandomIntFromAList = fixture(1..5)

You can also generate an infinite sequence of a type, which you can then filter:

val fixture = kotlinFixture()

val intSequence = fixture.asSequence<Int>()

// Standard Kotlin sequence functions can then be applied before using
// the sequence through an iterator for access to the next() function.

// For example, you can filter values
val oddIterator = intSequence.filter { it.absoluteValue.rem(2) == 1 }.iterator()
val oddNumber = oddIterator.next()
val anotherOddNumber = oddIterator.next()

// Or, ensure it returns only distinct values
enum class XYZ { X, Y, Z }
val enumIterator = fixture.asSequence<XYZ>().distinct().iterator()
val aDistinctValue = enumIterator.next()
val anotherDistinctValue = enumIterator.next()

⚠️

The sequence can hang indefinitely if the applied operators prevent the generation of new values. For example: distinct will hang if we exhaust all available values. A good practice is to add a take(count) which will throw a NoSuchElementException if we try to generate more values. filter that can never be fulfilled e.g. filter { false }

Configuration options

Everything can be customised, see configuration options for more details.

Advanced engine customisation is also possible if the above options are not enough.

Kotest integration: property based testing

The library provides KotlinFixture powered property based testing for Kotest.

See Kotest integration for more details.

Java Faker integration: pretty data

Generate values with a closer match to real data using Java Faker.

See Java Faker integration for more details.

Generex integration: regex to random string

To generate a random string from a regular expression, look no further than the Generex integration.

See Generex integration for more details.

Related projects

• Marcello Galhardo’s Kotlin.Fixture.

• FlexTrade’s KFixture wrapper for JFixture.

• Jeasy’s Easy Random.

Please take a look at the feature comparison with related projects.

Contributing

Please fork this repository and contribute back using pull requests.

All contributions, large or small, major features, bug fixes, additional language translations, unit/integration tests are welcome.

License

Copyright 2021 Appmattus Limited

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at https://www.apache.org/licenses/LICENSE-2.0.

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.