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overview | mocks | utilities | macros | fine points | development


then | thenReturned | thenThrown | when

Traditionally, test written in BDD fashion has 3 sections: given, when, then. Those sections are preceded by comments. Example test could look like this.

public class ArrayListTest {
  private List<Object> list;

  public void is_not_empty_after_adding_first_element() {
    // given
    list = new ArrayList<>();

    // when

    // then

Testory makes your tests more human-readable. It provides family of given, when, then methods that make those sections explicit.

import static org.testory.Testory.*;

public class ArrayListTest {
  private List<Object> list;

  public void is_not_empty_after_adding_first_element() {
    given(list = new ArrayList<>());

This family has plenty of overloaded methods to cover scenarios like asserting exceptions, accepting matchers, stubbing and verifying mocks and more.


then methods allow you to assert that specific condition is true. These are similar to junit assertion methods.

  • then(boolean) is like assertTrue(boolean)
  • then(Object, Object) is like assertThat(T, Matcher<T>)
  • thenEqual(Object, Object) is like assertEquals(Object, Object)

Those are standalone assertions, which means they do not rely on what happened at when line like other assertions do.


Expression nested in when method usually returns a result. You can assert your expectation about this result using thenReturned method. Assertion fails if actual result is not equal to expected Object or value.

given(list = asList("element"));

If you need more complicated logic than equals you can use Matchers from external libraries.

given(list = asList("element"));


Expression nested in when can also throw Throwable. Normally it would make a test fail, but sometimes Throwable is exactly what you expect. Classic idiom for asserting that throwable was thrown uses try-catch clause.

list = asList();
try {
} catch (IndexOutOfBoundsException e) {}

Testory can catch Throwable for you, but you need to help by wrapping tested expression in lambda. After that you can assert that caught Throwable meets you expectations.

given(list = asList());
when(() -> list.get(0));

thenThrown is overloaded to accept Throwable instance, Class or matcher. Of course assertion fails if expression did not throw anything.


Asserting result of void method also requires help, because you cannot nest void expression as an argument. You need to wrap an expression in lambda, even if you don't need to catch throwable. And because now throwable is caught, it will not make test fail as usual. To restore this behavior, you need to assert explicitly that you expect expression to not throw anything, using thenReturned().

given(list = new ArrayList<>());
when(() -> list.clear());

There is an alternative to using lambdas. It involves invoking method on proxy returned by when.

given(list = asList());

given(list = new ArrayList<String>());

If you can't use lambdas (you do not use java8), this looks like better alternative than using expanded anonymous classes. However there is a downside, because not all types are proxiable (for example final classes). In that case, when returns null and you get NullPointerException. Also final methods are not proxied, which results in unpredictable behavior. Additionally static calls cannot be written this way, because there is no this to wrap in proxy.


stubbing | verifying | matching invocations | spying

Testory is a full-featured mocking framework with intuitive grammar. Mocks are programmable objects inheriting interface from specific type. You create a mock by providing class or interface.

given(list = mock(List.class));


Stubbing is telling a mock what should happen if particular invocation occurs. You need to define what invocation you are talking about (what mock, which method with what arguments). Also you need to define what should happen on invocation (return object, throw throwable).

One way to specify invocation is by providing mock, method and arguments explicitly. More complex ways are described in matching invocations section. Thing that can happen on invocation can be as simple as returning an object. For example, if you want list.get(1) to return object, you stub it using willReturn(object).

given(willReturn(object), list).get(1);

If you want to stub void method to just return without throwing, use willReturn(null).

given(willReturn(null)), list).clear();

Other thing that can happen on invocation is throwing Throwable. For this purpose use willThrow.

given(willThrow(new IndexOutOfBoundsException()), list).get(2);

Throwing throwable preserves original stack trace which may be inconvenient during debugging. Using willRethrow fills in stack trace upon throwing.

given(willRethrow(new IndexOutOfBoundsException()), list).get(2);

If you need more complex logic to happen on invocation, implement custom Handler.

given((invocation -> {
  Method method = invocation.method;
  Object instance = invocation.instance;
  List<Object> arguments =  invocation.arguments;
  if(...) {
    return ...
  } else {
    throw ...
}), list).get(0);

If you stub a mock to return object incompatible with method return type, or throw throwable incompatible with method signature, you will get ProxyException upon invocation.

You can restub already stubbed invocation, because most recent stubbing takes precedence over earlier one. Newly created mock is already stubbed for convenience. equals/hashCode is stubbed, so mock is equal only to itself. toString is stubbed to contain class name and unique ordinal.

If mock is instance of Throwable then additional methods are stubbed. fillInStackTrace is stubbed to return this instance. All overloadings of printStackTrace are stubbed to print mock's name.

All other methods are stubbed to return null (or binary zero for primitive types). Those default stubbings can be restubbed as any other stubbing.


Additionally to being stubbable, mocks remember invocations that happened on them. You can use this feature to assert your expectations about how tested object should collaborate with its dependencies. Simplest way is to define your expectation by using thenCalled and providing mock, method and arguments of expected invocation. For example, FilterOutputStream (tested class), when being closed, should also close OutputStream it decorates.

given(output = mock(OutputStream.class));
given(filterOutput = new FilterOutputStream(output));

By default, invocation is expected to be called exactly once. Assertion fails if there are none or more than one matching invocations. You can verify other number of invocations by passing exact value (may be 0).

thenCalledTimes(3, mock).size();

You can also use matcher to be more flexible about number of invocations.

thenCalledTimes(greaterThan(0), mock).toString();

By default, order of invocations does not matter. If you need to assert that invocations happened in order, use ordered verifying.


Matching Invocations

In previous examples of stubbing and verifying we always specified invocation by providing exact mock, method and arguments. Sometimes you don't care about arguments. It this situation, you can use any as a placeholder for arguments you don't care about. For example, asserting that add method was called on mock list with any argument.


If you don't want to specify exact argument, but still care about its value, you can provide matcher.

thenCalled(list).add(any(Object.class, startsWith("prefix")));

Class passed to any is just for type inferring. Argument can be instance of any type and still can match. If you want to match arguments that can be assigned to specific type, use anyInstanceOf.


In most cases you can mix any with real arguments.

thenCalled(list).add(0, any(Object.class));

In cases where you cannot (due to technical limitations of primitives) TestoryException is thrown.

// throws TestoryException
given(willReturn(true), mock).someMethod(any(int.class), intValue);

You can workaround those cases by wrapping primitive values in a.

given(willReturn(true), mock).someMethod(any(int.class), a(intValue));

Use the shortcut if you expect exactly same instance

given(willReturn(true), mock).someMethod(the(instance));

Above examples work well if you know exact mock and method of invocation. Sometimes you want to be less specific than that. You can take full control of matching invocations by implementing your own InvocationMatcher. It is functional interface that answers, whether particular invocation is one you are interested about. Using this interface you can stub or verify invocation on more than one method, or even more than one mock, at once.

InvocationMatcher onCondition = new InvocationMatcher() {
  public boolean matches(Invocation invocation) {
    // custom logic

There are some built-in invocation matchers to support most popular idioms. By convention they start with on prefix. For example, you want to assert that there were no interactions on mock, meaning none of its methods was called. Asserting that there were no invocations on each method one by one would be tedious. You can achieve it using onInstance invocation matcher in combination with thenCalledNever assertion.


There are times when tested object has many collaborators and they are subjects to constant change. You want to write test in manner that would not require to correct stubbings every time a method is moved from one collaborator to another. This is usual for projects using service or dao objects. Solution is to stub mocks in a way, that does not care about mock, but only about return type (and arguments). See komarro library for more on the topic.

given(willReturn(person), onReturn(Person.class));
given(willReturn(person), onRequest(Person.class, "username"));


Spy is a mixture of real object and mock. Technically it is a mock, which means it can be stubbed and verified like any other mock. Difference is that at creation, spy is provided with spied object. Any invocation on spy will be delegated to spied object, unless that invocation was restubbed.

Spies can be used in situations where you would like to assert that invocation happened on object that is not a mock. Replacing object by mock would not achieve a goal, because object would lose its original non-mocky behavior. For example, you test method that copies data from one stream to another. You want to assert that method closes streams when done. This would require streams to be mocks. On the other hand input stream has to have real data, otherwise copy method would never reach the end of stream. This is possible by spying on real streams.

given(input = spy(new ByteArrayInputStream(new byte[] { 1, 2, 3 })));
given(output = spy(new ByteArrayOutputStream()));
when(copy(input, output));

Also you can stub an existing mock to act as a spy using willSpy handler.

given(real = new ByteArrayInputStream(new byte[] { 1, 2, 3 }));
given(input = mock(InputStream.class));
given(willSpy(real), onInstance(input));

Real object does not have to be actually real, it can be other mock/spy. There can be many spies for same real object.




Wherever api method accepts Object via parameter named matcher, you are free to pass any compatible matcher

    Object matcher = new Object() {
      public boolean matches(Object item) {
        return ...;


givenTimes | givenTry | givenTest

Macros help you remove boilerplate code from your tests.


Repeats invocation many times.

given(list = new ArrayList<String>());
givenTimes(5, list).add("element");


Catches possible Throwable thrown by chained method allowing test to run forward.

given(list = new ArrayList<String>());
givenTry(list).add(5, "element");


(this feature is in beta)

Initializes each field of this test and fails if initialization of any field fails.

public void before() {

Field is ignored if

  • field is primitive already assigned to something other than binary zero
  • field is reference already assigned to something other than null
  • field is final
  • field is static
  • field is not declared in this test's class but in it's superclass

Initialization depends on type of field.

Field of array type is initialized to array of size 1. Array's cell is initialized recursively.

Field of non-final type is assigned to mock. Mock is conveniently prestubbed

  • instance of Object is prestubbed.
    • toString is stubbed to return name of field
    • equals is stubbed so mock is equal only to itself
    • hashCode is stubbed to obey contract
  • instance of Throwable is additionally prestubbed
    • fillInStackTrace is stubbed to return this instance
    • printStackTrace is stubbed to print mock's name to relevant stream

Field of final type is assigned to sample data

  • boolean, Boolean is assigned to random value.
  • char, Character is assigned to random lowercase letter.
  • byte, Byte, short, Short, int, Integer, long, Long is assigned to random value such as
    • value * value * value does not cause overflow
    • is not equal to any of: -1, 0, 1
  • float, Float, double, Double is assigned to random value such as
    • value * value * value does not cause overflow or underflow
    • is not equal to +0.0 or -0.0
  • String is initialized to name of field.
  • enum is initialized to random constant.
  • Class is initialized to some sample class.
  • Field, Method and Constructor is assigned to member of sample class.

Random sample data is deterministically generated using field type and field name as a seed.

Fine Points

arrays | primitives | finals | concurrency |purging | api | class loader


In java, arrays are objects and invoking equals performs identity comparison. For sake of convenience, testory treats arrays as values and performs deep equals. This happens in

  • thenReturned
  • thenEqual
  • stubbing (comparing arguments)
  • verifying (comparing arguments)

Error messages also print contents of array where possible.


For convenience, testory does not differentiate between primitives and wrapper types. Necessary boxing/unboxing is performed behind the scenes. This applies to type of

  • object passed to when
  • object returned from chained when
  • object returned from Closure
  • object expected by thenReturned
  • objects compared by thenEqual
  • object matched by then
  • object returned from Handler (including object passed to willReturn)
  • object passed to a


Due to technical limitations, testory does not play well with final classes and final methods.

Final classes cannot be mocked or chained. Any of the following throws exception.

  • mock(FinalClass.class)
  • when(instanceOfFinalClass).method()
  • givenTry(instanceOfFinalClass).method()
  • givenTimes(instanceOfFinalClass).method()

Final methods on mock should not be invoked, stubbed or verified. Final methods on any object should not be proxied (used in chained form). Any of the following invokes real method on unreal (mocked/proxied) object causing undetermined effects!

  • mock.finalMethod()
  • given(willReturn(object), mock).finalMethod()
  • thenCalled(mock).finalMethod()
  • when(instance).finalMethod()
  • givenTry(instance).finalMethod()
  • givenTimes(n, instance).finalMethod()


Testory api is accessed through static methods. To make it thread-safe, testory maintains ThreadLocal state that contains all stubbings and invocations on mocks. This way you can execute tests in parallel and state visible by one thread is separated from other threads.

Traditionally tests are executed using single thread (let's call it main thread). For example, junit relies on assertions being called in main thread. Testory similarly assumes that mocking, stubbing and verification is done in main thread. However, once mock is created, it can be shared and accessed concurrently from any thread. Other threads will see stubbed behavior and interactions on mocks done from other threads will be verifiable by main thread. But to make it work you need to ensure happens-before relationship between stubbing, other thread code and verification. If you stubbed mock with custom Handler, then you are responsible to make that handler thread-safe.


(this feature is in beta)

Testory maintains global state that holds information about every mock, stubbing and invocation. This data needs to be periodically freed up. One reason is to prevent running out of memory. Other is to prevent invocations from previous tests to pollute verification and error messages of next test.

Since testory has no foolproof way to tell whether one test ended and another started, it relies on some simplistic assumption. Test should contain any number of given methods followed by single when method followed by any number of then methods. Thus calling given/when will purge last occurrence of when/then and everything before.

Purging has consequences. If purge was triggered by given, then there is no result to assert and calling thenReturned/thenThrown will throw an exception. Any mock created before purge becomes unusable. You will get an exception if you try to stub, verify, or call any method. Purged stubbing is no longer in effect even if it applies to mocks that were not purged. Purged invocations are not included during verification and are not included in error messages.


Adding testory to your classpath gives you access to many public classes. However, not all of them are intended for external use. Thus, testory clarifies which classes are exposed as public API. If class is exposed, you can rely on it's functionality along major version.

org.testory.Testory is exposed as it is the main entry point to library. You make testory methods available by statically importing Testory class.

import static org.testory.Testory.*;

If class is exposed, it recursively exposes all classes available through it's public methods. It includes types of parameters, return types and annotations of those methods.

For sake of clarity, all exposed types are enumerated below.

  • org.testory.Testory - main entry point to library containing static methods
  • org.testory.TestoryException - exception thrown when you misuse testory api
  • org.testory.TestoryAssertionError - error thrown when assertion fails causing test to fail
  • org.testory.common.Closure - functional interface representing piece of code returning Object or throwing Throwable
  • org.testory.common.VoidClosure - functional interface representing piece of code returning void or throwing Throwable
  • org.testory.common.Nullable - annotation that marks optional parameters and return values
  • org.testory.proxy.Invocation - represents invocation on mock (method, instance and arguments)
  • org.testory.proxy.Handler - represents logic executed when invoking method on mock
  • org.testory.proxy.InvocationMatcher - predicate for matching invocation on mock when you stub/verify
  • org.testory.proxy.ProxyException - exception thrown when misusing mocking api

Deprecated classes that will be removed in next major version.

  • org.testory.Closure - deprecated alias for org.testory.common.Closure

Beta features are exception to those rules. They can be removed at any time without incrementing major version.


Testory relies on generated bytecode to support some features, mocking in particular. Bytecode is loaded using ClassLoader. Which class loader is used will affect loaded Class visibility and scope. There are different strategies for class loader selection observed in different libraries. The one testory chose is to always use Thread.currentThread().getContextClassLoader(). This way caller has full control and full responsibility for class loading by setting context class loader using Thread.currentThread().setContextClassLoader().

When you mock a class, testory uses class loader you provided to load generated bytecode. This bytecode has a form of a class that extends class you mocked. Class loader you provided will try to recursively find all parent classes in hierarchy. For this to succeed, parent classes need to be visible from your class loader. This requires your class loader to be same as, or child of, class loader that loaded parent class. Failing to properly set class loader may cause some runtime errors, like NoClassDefFoundError, package *** does not exist or java.lang.ClassNotFoundException:$Factory


building | contributing


You can build testory.jar by running bash script ./run/build from project directory. Since 1.0.0 build is deterministic. This means you get identical testory.jar file every time. If you build version that has a release tag (like v1.0.0), it should be identical to released file.


If you found a bug, have an idea for a new feature, or just a question, please post it as github issue.

If you want to contribute a code, please do not use github's pull request feature. Just publish changes anywhere and post a link to your repository in relevant issue. Simplest way is to fork testory repository on github.