Custom Assertions...when assertEquals() is not enough

Tomek Kaczanowski

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A 15 minutes„lightning talk”

● Developer● Blogger● Books author

twitter: @tkaczanowskihttp://practicalunittesting.com

Tomek Kaczanowski

Expectations

our tests should:● verify

americanmethod.com

Expectations

our tests should:● verify● be readable

code.tutsplus.com

Expectations

our tests should:● verify● tell a story

jasonfurnell.wordpress.com

Expectations

our tests should:● verify● tell a story● be focused

noble.org

Expectations

our assertions should:● verify● tell a story● be focused

The Evolution of Assertions

The Evolution of Assertions

The Evolution of Assertions

The Evolution of Assertions

The Evolution of Assertions

Talk is cheap.Show me the code.

assertThat(...)

assertThat(...)

assertThat(...)

The Anatomy of Custom Assertion

The Anatomy of Custom Assertion

The Anatomy of Custom Assertion

Custom Assertions or Private Methods?

verifySuccessfulRedirect(response, FALLBACK_URL);

dashboardShows(dashboardPage, „my campaign”, „Target”, „PL”);

noHits(„2007-06-06 02:00”);noHits(„2007-06-06 03:00”);hitsAndRevenue(„2007-06-06 04:00”, 2, 7);...

Real Life Examples

Real Life Examples

actual

Real Life Examples

actual

assertThat(found) .overwritingErrorMessage( „expected row for {} but found only rows for {}”, stringDate, dates(actual) ) .isTrue();

Real Life Examples

actual

Conclusions

Upsides

● readable● reusable● simple to write● cheap to maintain

Upsides and Downsides

● need to write them● can hide bad smells

● readable● reusable● simple to write● cheap to maintain

Best Practices

use AssertJ• forget about JUnit/TestNG assertions

introduce custom assertions• when private methods are not good enough• if you care about ubiquitous language• when “then” part is getting huge • to impress/confuse your team mates

The Evolution of Assertions

The Evolution of Assertions

Links

AssertJ: http://joel-costigliola.github.io/assertj/

tools used to prepare these slides• http://shaky.github.bushong.net/• http://hilite.me/• http://asciiflow.com

Thank you!

You can learn more about writing high quality tests by

reading my books: „Practical Unit Testing”

and„Bad Tests, Good Tests”.

Please visithttp://practicalunittesting.com

to learn more.