Clean Test Code

David Völkel, @davidvoelkel
Clean Test Code
Agile Testing Days 11.11.2014

2
@davidvoelkel
Dev & Consultant
Software Craftsman
Test-Driven Development
Software Design
@softwerkskammer

Dirty Test Code
technical debt
velocity decrease
costs
latency
agile

Clean Tests
4 attributes reliable readable redundancy-free focused Conclusion Q&A

xUnit- Patterns
BDD
Functional tests
setup
arrange
given
Input rows
execute
act
when
“Fixture“
verify
assert
then
Output rows
[teardown]
[annihilate]
Test Phases
Input
Output

Reliable
Mind complexity, so avoid
•boolean assertions
assertTrue(age >= 18);
assertThat(age, greaterThan(17))

Reliable
Mind complexity, so avoid
•boolean assertions
•conditionals & complex loops
boolean containsName = false;
for (String name: names) {
if (name.equals("David")) {
containsName = true;
}
}
assertTrue(containsName);
assertThat(names, hasItem("David"));

Readable
Read >> write
Executable specifications
Living documentation

Abstraction
avoid irrelevant details

Test Method Body
Gerard Meszaros:
„When it is not important for something to be seen in the test method, it is important that it not be seen in the test method! “

“In the order form the user should be able to finish the order process by pressing the cancel button”

@Test public void cancelProcess_inOrderForm() {
server.runningProcesses(0);
ProcessStatus process = server.startProcess(Process.ORDER);
processInstanceId = process.getInstanceId();
server.expectUserForm(processInstanceId, ORDER_FORM);
Form form = new Form();
form.setOrderDate("01.01.2015");
form.setStandardDelivery(false);
String taskId = server.taskIdFor(processInstanceId);
controller.submit(form,
Mockito.mock(BindingResult.class), null,
taskId, null, CANCEL);
}

ProcessStatus process = server.startProcess(Process.ORDER);
}
„Testscript“
“Incidental Details”

ProcessStatus process = server.stareProcess(Process.ORDER);
}
FORM
CANCEL
Signal-Noise-Ratio?
Single Level of Abstraction?

inForm(ORDER_FORM);
submitFormWithButton(CANCEL);
noProcessRunning();
}

Test class names
public class AnOrderProcess {
OrderProcess process;
@Before public void createOrderProcess() {
process = new OrderProcess();
}
object under test

}
@Test public void inOrderForm_cancel() {
process.setState(ORDER_FORM);
process.submit(CANCEL_BUTTON);
assertThat("process canceled", process.isCanceled(), equalTo(true));
}
Test method names
object under test

}
}
Test method names
object under test
setup

}
}
Test method names
setup
execute

}
}
Test method names
setup
execute
verify

Audience?
test maintainer
search test failure cause
business

Communicate
comprehensively
OuT + setup + execute + verify
Distribute: Class, method name, verify

Hierarchical tests
}
public class InOrderForm {
@Before public void inOrderForm() {
}
@Test public void whenCanceled_processIsStopped() {
assertThat("process stopped", process.isStopped(), equalTo(true));
}
@Test public void whenBought_orderIsConfirmed() {
process.submit(BUY_NOW_BUTTON);
assertThat("state", process.getState(), equalTo(ORDER_CONFIRMED));
}
}
…
extract common
setup

OuT
Hierarchical tests
setup
execute
verify

Helper methods
Object Mother
Test Data Builder
aCustomer("David");
CustomerTest.aCustomer("David");
CustomerMother.aCustomer("David");
CustomerMother.aCustomer("David", „Völkel");
CustomerMother.aCustomer(null, „Völkel", null, null, null, null, birthday);
aCustomer().withLastName("Völkel")
.withBirthDay(birthDay)
.build();
Common test data

void assertMoneyEquals(Money expected, Money actual) {
assertEquals("currency", expected.getCurrency(),actual.getCurrency());
assertEquals("amount", expected.getAmount(), actual.getAmount());
}
Matcher<Money> equalTo(Money money) {
return allOf(
property(money, Money::getCurrency, "currency"),
property(money, Money::getAmount, "amount"));
}
Custom asserts via helper methods
Composed Hamcrest Matchers
Common verify

"Single Concept per Test"
"One Execute per Test"
"One Assert per Test"
Focused

State vs. testability
Focused

„Listen to your tests!“
Hard-to-test Code

Clean Tests
1.reliable
2.readable
3.redundancy-free
4.focussed

Resources
Books
„Clean Code“, Robert C. Martin
„xUnit Test Patterns“, Gerard Meszaros
„Effective Unittesting“, Lasse Koskela
„Growing Object Oriented Software“, Steve Freeman, Nat Pryce
„Specification by Example”, Gojko Adzic
Videos
Episodes 20-22 http://cleancoders.com/,
Robert C. Martin

David Völkel
codecentric AG
Twitter: @davidvoelkel
david.voelkel@codecentric.de
www.codecentric.de
blog.codecentric.de
Q&A
35

Creative Commons ShareAlike 4.0
The images used are public domain and can be found on Wikipedia.
License
36

Clean Test Code

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