ReSample - A Test Fixture Generator

Table of Contents

1. Overview
2. Features
3. How to use
4. Suppliers
5. Scope hierarchy
6. Auto-sampling
7. How to contribute

Overview

ReSample is a small library that creates sample instances of Java Beans by filling in data from configurable factories. This simplifies creation of test fixtures to be used in unit tests. Fixtures can be used to apply the ObjectMother-Pattern (https://martinfowler.com/bliki/ObjectMother.html).

This library reduces the overhead of creating fixtures by initializing the complete object with valid (non-null) values. This way you can focus on the data needed for the test case rather than setting all required values by hand to not break not-null constraints for example.

ReSample is intended to always return static test data values. It is not the purpose of ReSample to generate random test data.

Example

The following example demonstrates how to generate a sample instance of Person.

	class Person {
		private String name;
		private String forname;
		private int age;
		private LocalDate brithday;
		private Gender gender;

		// Default Constructor
		// Getter / Setter...
	}

	enum Gender {
		MALE,
		FEMALE,
		UNKOWN;
	}


	@Test
	public void shouldGenerateSampleData() {
	  Person person = Samples.of(Person.class)
	      .checkForNullFields()
	      .useForEnum(enumValueSupplier())
	      .use(fieldNameStringSupplier())
	      .forType(String.class)
	      .use(localDateSupplier(2018, 8, 30))
	      .forField(Person::getBrithday)
	      .newInstance();
	  System.out.println(person);
	}

The above example will generate a Person instance with the follwing values:

Person [name=name, forname=forname, age=0, brithday=2018-08-30, gender=MALE]

Features

ReSample provides the following features to create test data fixtures:

• Primitive types are initialized with default values out-of-the-box.
• Generation can be customized with value factories
  • Supported are supplier- or function-lambdas
• Factories can be registered for
  • types
  • fields
  • global (only for enumeration value suppliers)
• Factories can be obtained by
  • configuration builder
  • other Sample-instances
• Lists and Maps are supported
• Auto-sampling: Applies a configuration recursively to reduce configuration overhead.
• 2 Collection-Sampling-Modes:
  • Default: Sampling Collections and using bean field setter
  • JAXB-Support: Sampling Elements and adding all be using collection field getter
• Ready to use suppliers are shipped with this library
  • LocalDate supplier
  • Date supplier
  • ZonedDateTime supplier
  • TimeZone supplier
  • Generic enumeration supplier
  • String suppliers
  • Default value suppliers for primitive or wrapper types
  • even more...

How to use

	@Test
	public void shouldGenerateSampleData() {
		Person person = Samples.of(Person.class)
		    .checkForNullFields()
		    .useForEnum(enumValueSupplier())
		    .use(fieldNameStringSupplier())
		    .forType(String.class)
		    .use(localDateSupplier(2018, 8, 30))
		    .forField(Person::getBrithday)
		    .newInstance();
			System.out.println(person);
	}

The example above shows how to use the core functions of ReSample. Basically you can register supplier lambdas on a per type or per field basis. The fixture generator then creates a new instance of the specified type reflectively and applies all supplier lambdas. The suppliers are expected to create new values each time they are called. All field hit by the configuration will be access through setter methods to set the generated values.

ReSample can ensure that every property of the Java Bean was hit by a configuration. This way the generation aborts with an exception if the object is not completely initialized after data generation. This way it is easy to get notified if a field was added to the Java Bean but no sample value would be generated.

Suppliers

ReSample provides a set of ready-to-use suppliers. The following list may not be complete. For a full documentation of provided suppliers please have a look at the JavaDoc of com.remondis.resample.supplier.Suppliers or click here. There are suppliers for:

• long, int, short, byte, float, double, boolean for different default values
• enum values
• Date, LocalDate, ZonedDateTime
• BigDecimal

Suppliers can be extended by the user to implement special requirements.

If you miss a supplier implementation your PR ist very welcome! See How to contribute!

Scope hierarchy

ReSample defines a scope hierarchy that is used when applying value factories:

1. all primitive fields and lists (of respective wrapper types) are filled with default values.
2. all enumeration fields and lists are filled using the global enumeration value supplier
3. all fields and lists are filled using the suppliers registered for types
4. all configured fields are filled using the specified supplier
5. all fields holding maps are filled using the specified type and enum suppliers
6. all non-hit fields are processed by auto-sampling (if active)

Auto-sampling

ReSample supports auto-sampling which tries to reduce the configuration overhead for large object graphs. When auto-sampling is active the configuration is applied to all transitive references of the object graph. This way all Java Beans can be generated using one configuration.

How to contribute

Please refer to the project's contribution guide