Fluent Assertions

The juneau-assertions module in Juneau is a powerful API for performing fluent style assertions.

Fluent assertions have two types of methods:

asX methods which perform transformations.
isX methods which perform assertions.

Multiple transformations and assertions can be performed per statement.

Examples

import static org.apache.juneau.assertions.Assertions.*;
import static org.apache.juneau.assertions.AssertionPredicates.*;

// Check the contents of a string.
assertString("foo, bar")
    .asSplit(",")
    .asTrimmed()
    .is("foo", "bar");

// Extract a subset of properties from a list of beans and compare using JSON5.
List myListOfBeans = ...;
assertBeanList(myListOfBeans)
    .asPropertyMaps("a,b")
    .asJson().is("[{a:1,b:'foo'}]");

// Perform an arbitrary Predicate check against a bean.
MyBean myBean = ...;
assertBean(myBean)
    .is(x -> isValidCheck(x))

// Check that a list of strings has less than 10 entries and the first
// 3 entries are [foo, bar*, null] using assertion predicates.
List myListOfStrings = ...;
assertStringList(myListOfStrings)
    .asSize().isLt(10)
    .asFirst(3)
        .is(eq("foo"),match("bar*"),isNull())

// Check that an exception is thrown and is the specified type and has the specified message.
assertThrown(()->myBean.runBadMethod())
    .isExists()
    .isExactType(RuntimeException.class)
    .asMessage().is("foo");

The Assertions APIs are used throughout the REST client and server APIs for performing inline assertions on REST requests and responses.

Example

// Create a basic REST client with JSON support and download a bean.
MyBean bean = RestClient.create()
    .json5()
    .build()
    .get(URI)
    .run()
    .assertStatus().asCode().is(200)
    .assertHeader("Content-Type").isMatches("application/json*")
    .getContent().assertValue().asString().isContains("OK")
    .getContent().as(MyBean.class);