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Version: v1.0.x

Fixture Customization APIs

Fixture Monkey offers a range of APIs within the ArbitraryBuilder class that enable customization of objects created by it.

Customizing Fixtures​

set()​

The set() method is used to assign values to one or more properties referenced by the expression.

Different types, including Supplier, Arbitrary, ArbitraryBuilder, NOT_NULL, NULL, or Just can be used as the value. Additionally, a certain instance of an object can also be used as the value.

fixtureMonkey.giveMeBuilder(Product.class)
    .set("id", 1000);
Just​

Using an instance wrapped by Just when using set() makes you set the value directly instead of decomposing. Normally, when you set() a property in ArbitraryBuilder it does not use an instance of the given value, it does a deep copy instead. So, if you need to set with an instance, you can use Values.just(instance) This feature can be useful in cases where you need to set a property to a mock instance when using a mocking framework.

Note that you cannot set a child property after setting with Just.

Product product = fixture.giveMeBuilder(Product.class)
    .set("options", Values.just(List.of("red", "medium", "adult"))
    .set("options[0]", "blue")
    .sample();

For example, the product instance created above, will not have the value "blue" for the first element of options. It will remain the list given with Just.

size(), minSize(), maxSize()​

The size() method lets you specify the size of container properties. You have the flexibility to either set a precise size or specify a range using the minimum and maximum values.

Alternatively, you can use minSize() or maxSize() to set only the minimum or maximum container size. (By default, the size range is from 0 to 3 elements.)

fixtureMonkey.giveMeBuilder(Product.class)
    .size("options", 5); // size:5

fixtureMonkey.giveMeBuilder(Product.class)
    .size("options", 3, 5); // minSize:3, maxSize:5

fixtureMonkey.giveMeBuilder(Product.class)
    .minSize("options", 3); // minSize:3

fixtureMonkey.giveMeBuilder(Product.class)
    .maxSize("options", 5); // maxSize:5

setNull(), setNotNull()​

At times, you might want to ensure that a property is either always set to null or always has a value. In such situations, you can use setNull() or setNotNull().

fixtureMonkey.giveMeBuilder(Product.class)
    .setNull("id");

fixtureMonkey.giveMeBuilder(Product.class)
    .setNotNull("id");

setInner()​

With setInner() you can apply customizations defined within an InnerSpec instance to your builder. An InnerSpec is a type-independent specification for the customizations to be applied.

Instances of InnerSpec can be reused to consistently and easily configure nested properties. This feature is particularly beneficial when customizing map properties.

For additional guidance, refer to InnerSpec

InnerSpec innerSpec = new InnerSpec()
    .property("merchantInfo", it -> it.entry(1000, "ABC Store"));

fixtureMonkey.giveMeBuilder(Product.class)
    .setInner(innerSpec)

setLazy()​

The setLazy() function assigns the property a value obtained from the provided Supplier. The Supplier will run every time the ArbitraryBuilder is sampled.

This can be particularly useful when you need to generate unique sequential IDs or set the most recent value.

AtomicReference<Long> variable = new AtomicReference<>(0L);
ArbitraryBuilder<Long> builder = fixtureMonkey.giveMeBuilder(Long.class)
    .setLazy("$", () -> variable.getAndSet(variable.get() + 1));

Long actual1 = builder.sample(); // actual1 == 0
Long actual2 = builder.sample(); // actual2 == 1

setPostCondition()​

setPostCondition() can be used when your fixture needs to adhere to a specific condition. This condition can be defined by passing a predicate.

danger

Using setPostCondition can incur higher costs for narrow conditions. In such cases, it's recommended to use set instead.

fixtureMonkey.giveMeBuilder(Product.class)
    .setPostCondition("id", Long.class, it -> it > 0)

fixed()​

fixed() can be used when you want your arbitrary builder to consistently return instances with the same values every time it is sampled.

fixtureMonkey.giveMeBuilder(Product.class)
    .fixed()

limit​

For the set(), setLazy(), and setPostCondition() methods, you can include an additional parameter that determines the number of times the customization will be applied. This can be advantageous when the expression refers to multiple properties.

fixtureMonkey.giveMeBuilder(Product.class)
  .set("options[*]", "red", 2); // up to 2 elements in options will be set to "red"

Expanding Customization using Sampled Results​

thenApply()​

The thenApply() method becomes handy when you need to customize a field based on the sampled result of the builder. For instance, let's assume you want the "productName" field to match the generated "id" of the Product. You can use thenApply() as follows:

fixtureMonkey.giveMeBuilder(Product.class)
    .thenApply((it, builder) -> builder.set("productName", it.getId().toString()))

acceptIf()​

You might also find the need to perform additional customization based on a specific condition. In such cases, you can utilize the acceptIf() method, which applies the customization only when the predicate is satisfied.

fixtureMonkey.giveMeBuilder(Product.class)
    .acceptIf(
        it -> it.getProductType() == ProductType.CLOTHING,
        builder -> builder.set("price", 1000)
    )

Transforming the Type of ArbitraryBuilder​

map()​

The map() function is used to convert the ArbitraryBuilder type into another type.

fixtureMonkey.giveMeBuilder(Product.class)
    .map(Product::getId); // transforms to ArbitraryBuilder<Long>

zipWith()​

zipWith() becomes useful when you want to merge multiple ArbitraryBuilders to create an ArbitraryBuilder of a different type. You have to define how you intend to combine the builders.

ArbitraryBuilder<String> stringBuilder = fixtureMonkey.giveMeBuilder(String.class);

ArbitraryBuilder<String> zipped = fixtureMonkey.giveMeBuilder(Integer.class)
    .zipWith(stringBuilder, (integer, string) -> integer + "" + string);