Software Construction & Design 1
The University of Sydney Page 1
Software Design and
Construction 2
SOFT3202 / COMP9202
Advanced Testing
Techniques (1)
School of Information Technologies
Dr. Basem Suleiman
The University of Sydney Page 2
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Agenda
– Testing Types
– Integration Testing, Regression Testing
– Advanced Testing Techniques
– Test doubles (Dummies, Fakes, Stubs, Spies, Mocks)
– Contract Test
– Testing Frameworks
– Mockito
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Advanced Testing Types
Integration testing, regression testing
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Software Components/Sub-systems
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Integration Testing
– The process of verifying interactions/communications among software
components behave according to its specifications
– Independently developed (and tested) units may not behave correctly when
they interact with each other
– Activate corresponding components and run high-level tests
– Incremental integration testing vs. “Big Bang” testing
.
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Interaction Errors
– Parameter interfaces
– Methods in objects have a parameter interface
– Procedural interfaces
– Objects and reusable components
– Message passing interfaces
– One component encapsulates a service from another component by passing a
message to it
– Shared memory interfaces
– Interfaces in which block of memory is shared between components (e.g.,
embedded systems)
.
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Your Testing Exposed Bugs
– What would you do when your testing reveal bugs/errors?
– You fixed the discovered bugs, what should happen next?
– You extended one class with additional functionality (new feature), what
should happen next?
.
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Regression Testing
– Verifies that the software behaviour has not changed by incremental
changes to the software
– Bug fixes, code extension, code enhancements
– Modern software development processes are iterative/incremental
– Changes may be introduced which may affect the validity of previous tests
– Regression testing is to verify
– Pre-tested functionality (and non-functional properties) still working as expected
– No new bugs are introduced
.
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Regression Testing – Techniques
. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.460.5875&rep=rep1&type=pdf
Type Description
Retest All Re-run all the test cases in a test suit
Test Selection Re-run certain test cases based on the changes in the code
Test case
prioritization
Re-run test cases in order of its priority; high, medium, low. Priority
determined by how criticality and impact of test cases on the product
Hybrid Re-run selected test cases based on it’s priority
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Test-Driven Development
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Test-driven Development
– A software development approach for developing the code incrementally
along with a set of tests for that increment
– Write tests before code
– All tests must pass before starting the next increment
– Introduced in the XP agile development method
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TDD Cycle
– “A rapid cycle of testing, coding, and refactoring”
– Kent Beck
– “Every few minutes, TDD provides proven code
that has been tested, designed, and coded”
– Red, Green, Refactor cycle
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TDD Cycle – Think
– Think of a behavior you want your code to have(small
increment; few lines of code)
– Think of atest (few lines of code) that will fail unless the
behavior is present
– Pair programming helps
– Driver and navigator
..
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TDD Cycle – Red (Run the Test)
– Write the tests – only enough code for the current
increment of behavior
– Typically less than 5 lines of code
– Code for the class behavior and its public interface
(encapsulation)
– Tests use method and class names do not exist yet
– Run your entire suite of tests and enjoy the test failure
– Results in Red progress bar (testing tools)
..
https://www.jamesshore.com/Agile-Book/test_driven_development.html
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TDD Cycle – Green (Write Code)
– Write the code; just enough to get the test to pass
– Less than 5 lines
– It’s okay to hard code, you’ll refactor
– Run your tests again, and enjoy the tests passing
– Results in Green progress bar (testing tools)
..
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TDD Cycle – Refactor
– Review the code and look for possible improvements
– Ask your navigator if they made any notes
– Series of very small refactorings
– 1-2 minutes each, no longer than 5 minutes
– Run the tests after each refactoring
– Should always be green (pass!)
– Test failed and no obvious answer, get back to good code
– Refactor many times, improve design
– Refactoring isn’t about changing behavior
..
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TDD Cycle – Repeat
– Repeat to add new behavior, start the cycle over again
– Tiny bit of well-tested, well-designed code will be incrementally
created
– Typically, run through several cycles very quickly, then spend
more time on refactoring
– Do not skip any step, especially refactoring, to speed up!
..
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TDD – Red, Green, Refactor
– Use Red, Green, Refactor cycle to impalement TDD
– Think of a code behavior, then choose a small increment and
then a test
– Write the test for the current increment code and run the entire
suit of tests – should fail (Red bar)
– Write just enough code to get the test pass and run the tests
again – should pass (Green bar)
– Review the code and look for improvements – small set of
refactoring and run the tests after each (Refactor)
..
https://www.jamesshore.com/Agile-Book/test_driven_development.html
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TDD – Example
– Java class to parse HTTP query string (name-value pair)
– E.g., http://example.com/page/to/page?title=Central+Park&where=US
– Think
– “class to separate name/value pairs into a HashMap” or “class to put one
name/value pair into a HashpMap”? Why?
– Class QueryString won’t return a HashMap, but a method (valueFor(name)) to
access the name-value pairs. Shall you proceed with writing the test?
– Count() method instead to return total number of name-value pairs (more
suitable for one increment)
–
..
https://www.jamesshore.com/Agile-Book/test_driven_development.html
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TDD Example – Red Bar
..
public void testOneNameValuePair() {
QueryString qs = new QueryString(“name=value”);
assertEquals(1, qs.count());
}
public class QueryString {
public QueryString(String queryString) {}
public int count() { return 0; }
}
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TDD Example – Green Bar & Refractor
..
public int count() { return 1; }
Refactor
Change the QueryString name to HttpQuery() – noted for next cycle
Another test to try
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TDD Example – Repeat
..
public void testNoNameValuePairs() {
QueryString qs = new QueryString(“”);
assertEquals(0, qs.count());
}
Thinking
• Remove the hard-coded line but not time yet to deal with multiple query string
• Testing an empty string would require coding the count() properly
Emerging thoughts (noted for later cycles)
• Test the case of a null argument to the QueryString constructor
• Deal with the tests duplication tests that needed refactoring
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TDD Example – Green & Refactor
..
public class QueryString {
private String _query
public QueryString(string queryString) {
_query = queryString;
}
public int count() {
if (“”.equals(_query)) return 0;
else return 1;
}
}
Refactor (notes):
• Rename QuerySting
• testNull()
• Refactor duplicate tests
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TDD Example – testNull()
..
public void testNull() {
try {
QueryString qs = new QueryString(null);
fail(“Should throw exception”);
}
catch (NullPointerException e) {
// expected
}
}
• Test the case when the query string is null
• Red Bar – think of the behavior when the value is null
• Through an exception(Null is illegal) – simple design
public QueryString(String queryString) {
if (queryString == null) throw new
NullPointerException();
_query = queryString;
}
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TDD Example – valueFor()
..
public void testOneNameValuePair() {
QueryString qs = new
QueryString(“name=value”);
assertEquals(1, qs.count());
assertEquals(“value”,
qs.valueFor(“name”));
}
• Implement valueFor() method to return the associated value give a name/value pair
• Emerging thoughts: test for a name doesn’t exist (noted)
public String valueFor(String name) {
String[] nameAndValue =
_query.split(“=”);
return nameAndValue[1];
}
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TDD Example – Repeat
..
• Code passed the tests, but it was incomplete
• Multiple name/value pairs …
• Repeat …
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TDD – Benefits
– Help developers to understand the requirements and write better
code
– Simplify debugging
– Easier to find and fix mistakes in small code chunks
– Reduce cost of regression testing
– Improved design and code quality
– Research shows TDD substantially reduces the incidence of defects
– Reuse tests as the software grow, and use it as documentation
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Refactoring
– “Refactoring is the process of changing the design of your code without
changing its behavior” – Kent Beck
– Change the how not the what
– Refactoring is reversible!
– Analyze the design of existing code and improve it
– Code improvements can be identified with code smells
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How to Refactor
– Refactor constantly in a series of small transformations
– Learn from in-depth catalog of refactoring
– Refactor intuitively through learning the mindset behind refactoring
– Learn how to refactor manually
– Development frameworks/tools can help automating some refactoring
– Use continuous integration practices and automation tools
– Version control system, build and test automation, IDEs
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Test Double
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Movie – “Stunt Double”
https://i.ytimg.com/vi/xm7kzxXHF38/maxresdefault.jpg
http://cdn.kickvick.com/wp-content/uploads/2014/07/celebrity-stunt-doubles.jpg
https://amp.businessinsider.com/images/525328ce6bb3f78e7afdcbb2-750-563.jpg
https://i.ytimg.com/vi/xm7kzxXHF38/maxresdefault.jpg
http://cdn.kickvick.com/wp-content/uploads/2014/07/celebrity-stunt-doubles.jpg
https://amp.businessinsider.com/images/525328ce6bb3f78e7afdcbb2-750-563.jpg
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Test Double
– “A test double is an object that can stand in for a real object in a test, similar
to how a stunt double stands in for an actor in a movie” – Google Testing Blog
– Includes stubs, mocks and fakes
– Commonly referred to as “mocks”, but they have different uses!
– Why test double?
– Dependency on components that cannot be used
– Reduce complexity, test indecently
https://testing.googleblog.com/2013/07/testing-on-toilet-know-your-test-doubles.html
https://testing.googleblog.com/2013/07/testing-on-toilet-know-your-test-doubles.html
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Test Double – Types
Type Description
Dummy Pass object(s) that never actually used (to fill parameter list)
Stub Test-specific object(s) that provide indirect inputs into SUT
Spy Capture indirect output calls made by the SUT to another component
for later verification
Fake Objects to provide simpler implementation of a heavy component
Mock Object(s) that verify indirect output of the tested code
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Dummy Object
– Dummy, dummy parameter/value
– Pass object with no implementation (dummy) and never actually used
– E.g., Fill in parameter lists
– SUT’s methods to be called often take objects stored in instance variables
– Those objects, or some of its attributes, will never be used in the testing
– Preparing the SUT into right state (conform to the signature of some methods
need to be called)
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Dummy Object – Example
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(Test) Stub
– A test-specific object that provides indirect inputs during tests
– E.g., Object requires data from a database to answer a method call
– Used to verify logic independently when it depends on inputs from other
components
– Verify indirect inputs of the SUT
– It does not deal with indirect outputs of the system
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(Test) Stub – Example
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(Test) Spy
– Capture output calls made by the SUT to another component for later
verification
– Verify indirect outputs of the SUT
– Get enough visibility of the outputs generated by the SUT (observation
point)
– E.g., email service that records no. of messages sent
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(Test) Spy
– Capture output calls made by the SUT to another component for later
verification
– Verify indirect outputs of the SUT
– Get enough visibility of the outputs generated by the SUT (observation
point)
– E.g., email service that records no. of messages sent
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Fake (Object)
– Objects to provide simplified implementation of a heavy (real) component
– E.g., in-memory implementation of repository using simple collection to store
data
– SUT depends on other components that are unavailable or make testing
complex or slow
– Run tests faster
– Should not be used when want to control inputs to SUT or outputs of SUT
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Fake (Object) – Example
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Mock (Object)
– Object(s) that verify indirect output of the SUT
– E.g., function that calls email sending service, not to really send emails
but to verify that email sending service was called
– Calling real implementation during testing is tedious, or the side effect is not
the testing goal
– Unlike all doubles, mocks verify correctness against expectations
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Mock (Object) – Example
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Mock (Object)
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Test Doubles
– Understand the differences carefully and use the one that serve the
verification type and purpose and how it should be run
– Don’t be fooled by the mocking frameworks terminology – focus on the
verification purpose
– Read Fowler’s Mocks aren’t Stubs
– Check xUnit Test Patterns for more advanced details
https://martinfowler.com/articles/mocksArentStubs.html
http://xunitpatterns.com/
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Contract Test
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Test Double – External Services
– Test double to interact with external/remote service
– How accurate/reliable is a test double?
https://martinfowler.com/bliki/ContractTest.html
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Contract Test
– The process of running periodic tests against real components to check the
validity of test doubles results
– How?
– Run your own test against the double
– Periodically run separate contract tests (real tests to call the real service)
– Compare the results
– Check the test double in case of results inconsistency/failures
– Also, consider service contract changes
https://martinfowler.com/bliki/ContractTest.html
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Integrated (Broad) Tests
“Broad tests done with many modules active” – integrated testing
Read more for further discussion – https://martinfowler.com/bliki/IntegrationTest.html
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Collaborative (Narrow) Tests
Read more for further discussion – https://martinfowler.com/bliki/IntegrationTest.html
“Narrow tests of interaction with
individual test doubles” – Collaboration
Tests
“supported by Contract Tests to ensure
the faithfulness of the double” –
Contract Tests
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Integration Testing
Frameworks
Mockito
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Mocking Frameworks
– Mockito
– JMock
– EasyMock
– Mountebank
– Others …
http://www.mbtest.org/
http://jmock.org/
http://easymock.org/
http://www.mbtest.org/
http://jmock.org/
http://easymock.org/
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Mockito
– An open source testing (test spy) framework for Java
– It has a type called ‘spy’ which is partial mock1
– Verify interactions after executing tests (what you want)
– Not expect-run-verify (look for irrelevant interactions)
– Interaction among objects/components not unit testing
– Allows to specify order of verification (not all interactions)
https://github.com/mockito/mockito/wiki/FAQ
https://github.com/mockito/mockito/wiki/FAQ
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Mockito – Constructs
Mockito Features Description
mock(), @Mock or
Mokito.mock()
Different ways to create a mock
Answer or MockSettings Interfaces to specify how a mock should behave (optional)
when() Specify the mock to return a value when a method is called
Spy() or @Spy Caution: creates a (partial mock) for a given object
@InjectMocks automatically inject mcoks/spies annotated with @Mock() or
@Spy()
verify() Check methods were called with given arguments
http://static.javadoc.io/org.mockito/mockito-core/2.24.0/org/mockito/Mockito.html
Note: call MockitoAnnotations.initMocks(testClass) (usually in a @Before method) to get the annotations to work.
Alternatively, use MockitoJUnit4Runner as a JUnit runner
http://static.javadoc.io/org.mockito/mockito-core/2.24.0/org/mockito/stubbing/Answer.html
http://static.javadoc.io/org.mockito/mockito-core/2.24.0/org/mockito/MockSettings.html
http://static.javadoc.io/org.mockito/mockito-core/2.24.0/org/mockito/Mockito.html
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Mockito Example
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Mockito – Method Call
– Use Mockito.when() and thenRturn() to specify a behavior when a method is
called
– Example of methods supported in Mockito
Method Purpose
thenReturn(valueToBeReturned) Return a given value
thenThrow(Throwable tobeThrown) Throws given exception
Then(Answer answer) User created code to answer
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Mockito – ‘When’ Example
http://static.javadoc.io/org.mockito/mockito-core/2.24.0/org/mockito/Mockito.html#when-T-
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Mockito – Verifying Behavior
– Mockito.verify (T mockTobeVerified, verificationMode mode)
– Verifies certain behavior happened at least once (default) – e.g., a method is called once
– Different verification modes are available
Verification Mode Description
Times(int wantedNoCalls) Called exactly n times, default = 1
atMost(in maxNoOfCalls) Called at most n times
atLeast(int minNoOfCalls) Called at least n times
never() Never called
Timeout (int milliseconds) Interacted in a specified time range
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Mockito – Verifying Behavior Example
– Default mode is times (1) which can be omitted
– Argument passed are compared suing equals() method
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Mockito – Verifying Order of Calls
– InOrder (mocks) allows verifying mocks in order
– verify(mock): verifies interactions happened once in order
– verify(mock, VerificationMode mode): verifies interactions in order
http://static.javadoc.io/org.mockito/mockito-core/2.24.0/org/mockito/InOrder.html
http://static.javadoc.io/org.mockito/mockito-core/2.24.0/org/mockito/InOrder.html
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Writing Good Tests
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Writing Good Tests
– Reliable
– Free of bugs, defects or errors
– Fast
– Should not be counterproductive, will be run very frequently
– Keep it compact and readable
– Lots of refactoring
– Follow recommended coding practices (e.g., naming conventions, documentation)
– Cover wide range to show positive cases and errorenous code paths
https://github.com/mockito/mockito/wiki/How-to-write-good-tests
https://github.com/mockito/mockito/wiki/How-to-write-good-tests
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Writing Good Tests
– Do not mock everything
– It’s anti-pattern
– Understand mocking framework’s capabilities
– Mock syntax vs. actual purpose of mocking
– Read Fowler’s Mocks aren’t Stubs
– Do not mock type you do not own
– Third-party library or API – owner change the signature and behavior of the API
– Contract test ?
– Do not mock value objects
– Instantiating an object is too painful – not a valid reason
– Can be a sign that the code needs some serious refactoring or use builders for the value
objects (some tools such as Lombok can help)
https://github.com/mockito/mockito/wiki/How-to-write-good-tests
https://martinfowler.com/articles/mocksArentStubs.html
https://github.com/mockito/mockito/wiki/How-to-write-good-tests
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W4 Lecture: Advanced Testing
Techniques 2
W4 Tutorial + quiz
Next Lecture/Tutorial
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References
– Ian Sommerville. 2016. Software Engineering (10th ed.) Global Edition. Pearson
– James Shore and Shane Warden. 2007. The Art of Agile Development
– Martin Fowler, various testing articles. https://martinfowler.com/
– Gerard Meszaros, xUnit Test Patterns: Refactoring Test Code. Addison-Wesley
– Martin Fowler, Mocks Arent Stubs,
[https://martinfowler.com/articles/mocksArentStubs.html]
– Gaurav Duggal, Bharti Suri, Understanding Regression Testing Techniques.
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.460.5875&rep=rep1&t
ype=pdf
– Bernd Bruegge and Allen, H. Dutoit. 2009. Object-Oriented Software Engineering
Using Uml, Patterns, and Java (3rd ed.). Pearson
– Michal Lipski, Pragmatists: Test doubles: Fakes, Mocks and Stubs.
https://blog.pragmatists.com/test-doubles-fakes-mocks-and-stubs-1a7491dfa3da
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