org.inferred.testing.behavior

Class BehaviorTester

java.lang.Object

org.inferred.testing.behavior.BehaviorTester

public class BehaviorTester
extends Object

Convenience class for performing behavioral tests of API-generating annotation processors.

Behavior testing of generated APIs

Annotation processors that generate complex APIs from small template classes are difficult to write good tests for. For an example, take a processor that generates a builder for a class. Comparing generated source with a golden output, whether via exact line-by-line comparison, AST comparison or bytecode comparison, leads to fragile tests. Adding a new method—say, buildPartial()—or changing the way an unset field is represented internally—say, from a null value to an explicit boolean field—will break every test, even though the user-visible behavior is unaltered.

Additionally, as test code will not compile without the processor, compilation becomes part of the test. Moving part of the test out of JUnit loses convenient integration with a number of tools and ADEs.

Behavioral testing verifies the generated code by compiling and running a small Java test against it. Well-written behavioral tests will check specific contracts the code generator must honor—e.g. "the data object returned will contain the values set on the builder", or "an exception will be thrown if a field has not been set"—contracts that will continue to hold even as internal representations change, and new features are added.

BehaviorTester takes a set of annotation processors and Java classes, and runs the JVM's own compiler against them. It also takes test code, wraps it in a static method, compiles and invokes it. As we assume the classes and test code will not compile without the annotation processors, we take them in as strings, which may be hard-coded in the test or read in from a resource file. Here is an example for a hypothetical Builder generator:

 new BehaviorTester()
     .with(builderGeneratingProcessor)
     .with(new SourceBuilder()
         .addLine("package com.example;")
         .addLine("@%s public TestClass { ", MakeMeABuilder.class)
         .addLine("  private final %s<%s> strings;", List.class, String.class)
         .addLine("  TestClass(TestClassBuilder builder) {")
         .addLine("    strings = builder.getStrings();")
         .addLine("  }")
         .addLine("  public %s<%s> getStrings() {", List.class, String.class)
         .addLine("    return strings;")
         .addLine("  }")
         .addLine("}")
         .build())
     .with(new TestBuilder()
         .addLine("com.example.TestClass instance = new com.example.TestClassBuilder()")
         .addLine("    .addString(\"Foo\")")
         .addLine("    .addString(\"Bar\")")
         .addLine("    .build();")
         .addLine("assertEquals(\"Foo\", instance.getStrings().get(0));")
         .addLine("assertEquals(\"Bar\", instance.getStrings().get(1));")
         .build())
     runTest();
 

Constructor Summary

Constructors

Constructor and Description
BehaviorTester()

Method Summary

Methods

Modifier and Type	Method and Description
void	runTest() Compiles, loads and tests everything given to with(javax.annotation.processing.Processor).
BehaviorTester	with(JavaFileObject compilationUnit) Adds a JavaFileObject to pass to the compiler when runTest() is invoked.
BehaviorTester	with(Processor processor) Adds a Processor to pass to the compiler when runTest() is invoked.
BehaviorTester	withContextClassLoader() Ensures Thread.getContextClassLoader() will return a class loader containing the compiled sources.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BehaviorTester

public BehaviorTester()

Method Detail

with

public BehaviorTester with(Processor processor)

Adds a Processor to pass to the compiler when runTest() is invoked.

with

public BehaviorTester with(JavaFileObject compilationUnit)

Adds a JavaFileObject to pass to the compiler when runTest() is invoked.

See Also:

SourceBuilder, TestBuilder

withContextClassLoader

public BehaviorTester withContextClassLoader()

Ensures Thread.getContextClassLoader() will return a class loader containing the compiled sources. This is needed by some frameworks, e.g. GWT, but requires us to run tests on a separate thread, which complicates exceptions and stack traces.

runTest

public void runTest()

Compiles, loads and tests everything given to with(javax.annotation.processing.Processor).

Runs the compiler with the provided sources and processors. Loads the generated code into a classloader. Finds all @Test-annotated methods (e.g. those built by TestBuilder) and invokes them. Aggregates all exceptions, and propagates them to the caller.