So, you and your team have decided to make test automation a priority. You plan to use behavior-driven development to shift left with testing. You read the BDD 101 Series up through the previous post. You picked a good language for test automation. You even peeked at Cucumber-JVM or another BDD framework on your own. That’s great! Big steps! And now, you are ready to write your first Gherkin feature file. You fire open Atom with a Gherkin plugin or Notepad++ with a Gherkin UDL, you type “Given” on the first line, and…
Writer’s block. How am I supposed to write my Gherkin steps?
Good Gherkin feature files are not easy to write at first. Writing is definitely an art. With some basic pointers, and a bit of practice, Gherkin becomes easier. This post will cover how to write top-notch feature files. (Check the Automation Panda BDD page for the full table of contents.)
The Golden Gherkin Rule: Treat other readers as you would want to be treated. Write Gherkin so that people who don’t know the feature will understand it.
The biggest mistake BDD beginners make is writing Gherkin without a behavior-driven mindset. They often write feature files as if they are writing “traditional” procedure-driven functional tests: step-by-step instructions with actions and expected results. HP ALM, qTest, and many other test repository tools store tests in this format. These procedure-driven tests are often imperative and trace a path through the system that covers multiple behaviors. As a result, they may be unnecessarily long, which can delay failure investigation, increase maintenance costs, and create confusion.
For example, let’s consider a test that searches for images of pandas on Google. Below would be a reasonable test procedure:
- Open a web browser.
- Web browser opens successfully.
- Navigate to https://www.google.com/.
- The web page loads successfully and the Google image is visible.
- Enter “panda” in the search bar.
- Links related to “panda” are shown on the results page.
- Click on the “Images” link at the top of the results page.
- Images related to “panda” are shown on the results page.
I’ve seen many newbies translate a test like this into Gherkin like the following:
# BAD EXAMPLE! Do not copy. Feature: Google Searching Scenario: Google Image search shows pictures Given the user opens a web browser And the user navigates to "https://www.google.com/" When the user enters "panda" into the search bar Then links related to "panda" are shown on the results page When the user clicks on the "Images" link at the top of the results page Then images related to "panda" are shown on the results page
This scenario is terribly wrong. All that happened was that the author put BDD buzzwords in front of each step of the traditional test. This is not behavior-driven, it is still procedure-driven.
The first two steps are purely setup: they just go to Google, and they are strongly imperative. Since they don’t focus on the desired behavior, they can be reduced to one declarative step: “Given a web browser is at the Google home page.” This new step is friendlier to read.
After the Given step, there are two When-Then pairs. This is syntactically incorrect: Given-When-Then steps must appear in order and cannot repeat. A Given may not follow a When or Then, and a When may not follow a Then. The reason is simple: any single When-Then pair denotes an individual behavior. This makes it easy to see how, in the test above, there are actually two behaviors covered: (1) searching from the search bar, and (2) performing an image search. In Gherkin, one scenario covers one behavior. Thus, there should be two scenarios instead of one. Any time you want to write more than one When-Then pair, write separate scenarios instead. (Note: Some BDD frameworks may allow disordered steps, but it would nevertheless be anti-behavioral.)
This splitting technique also reveals unnecessary behavior coverage. For instance, the first behavior to search from the search bar may be covered in another feature file. I once saw a scenario with about 30 When-Then pairs, and many were duplicate behaviors.
Do not be tempted to arbitrarily reassign step types to make scenarios follow strict Given-When-Then ordering. Respect the integrity of the step types: Givens set up initial state, Whens perform an action, and Thens verify outcomes. In the example above, the first Then step could have been turned into a When step, but that would be incorrect because it makes an assertion. Step types are meant to be guide rails for writing good behavior scenarios.
The correct feature file would look something like this:
Feature: Google Searching Scenario: Search from the search bar Given a web browser is at the Google home page When the user enters "panda" into the search bar Then links related to "panda" are shown on the results page Scenario: Image search Given Google search results for "panda" are shown When the user clicks on the "Images" link at the top of the results page Then images related to "panda" are shown on the results page
The second behavior arguably needs the first behavior to run first because the second needs to start at the search result page. However, since that is merely setup for the behavior of image searching and is not part of it, the Given step in the second scenario can basically declare (declaratively) that the “panda” search must already be done. Of course, this means that the “panda” search would be run redundantly at test time, but the separation of scenarios guarantees behavior-level independence.
The Cardinal Rule of BDD: One Scenario, One Behavior!
Remember, behavior scenarios are more than tests – they also represent requirements and acceptance criteria. Good Gherkin comes from good behavior.
How you write a step matters. If you write a step poorly, it cannot easily be reused. Thankfully, some basic rules maintain consistent phrasing and maximum reusability.
Write all steps in third-person point of view. If first-person and third-person steps mix, scenarios become confusing. I even dedicated a whole blog post entirely to this point: Should Gherkin Steps Use First-Person or Third-Person? TL;DR: just use third-person at all times.
Write steps as a subject-predicate action phrase. It may tempting to leave parts of speech out of a step line for brevity, especially when using Ands and Buts, but partial phrases make steps ambiguous and more likely to be reused improperly. For example, consider the following example:
# BAD EXAMPLE! Do not copy. Feature: Google Searching Scenario: Google search result page elements Given the user navigates to the Google home page When the user entered "panda" at the search bar Then the results page shows links related to "panda" And image links for "panda" And video links for "panda"
The final two And steps lack the subject-predicate phrase format. Are the links meant to be subjects, meaning that they perform some action? Or, are they meant to be direct objects, meaning that they receive some action? Are they meant to be on the results page or not? What if someone else wrote a scenario for a different page that also had image and video links – could they reuse these steps? Writing steps without a clear subject and predicate is not only poor English but poor communication.
Also, use appropriate tense for each type of step. Givens should always use present perfect tense, and Whens and Thens should always use present tense. Rather than take a time warp back to middle school English class, let’s illustrate tense with a bad example:
# BAD EXAMPLE! Do not copy. Feature: Google Searching Scenario: Simple Google search Given the user navigates to the Google home page When the user entered "panda" at the search bar Then links related to "panda" will be shown on the results page
The Given step above indicates an action when it says, “The user navigates.” Actions imply the exercise of behavior. However, Given steps are meant to establish an initial state, not exercise a behavior. This may seem like a trivial nuance, but it can confuse feature file authors who may not be able to tell if a step is a Given or When. Using present perfect tense indicates a state rather than an action.
The When step above uses past tense when it says, “The user entered.” This indicates that an action has already happened. However, When steps should indicate that an action is presently happening. Plus, past tense here conflicts with the tenses used in the other steps.
The Then step above uses future tense when it says, “The results will be shown.” Future tense seems practical for Then steps because it indicates what the result should be after the current action is taken. However, future tense reinforces a procedure-driven approach because it treats the scenario as a time sequence. A behavior, on the other hand, is a present-tense aspect of the product or feature. Thus, it is better to write Then steps in the present tense.
The corrected example looks like this:
Feature: Google Searching Scenario: Simple Google search Given a web browser is at the Google home page When the user enters "panda" into the search bar Then links related to "panda" are shown on the results page
And note, all steps are written in third-person.
Another common misconception for beginners is thinking that Gherkin has an “Or” step for conditional or combinatorial logic. People may presume that Gherkin has “Or” because it has “And”, or perhaps programmers want to treat Gherkin like a structured language. However, Gherkin does not have an “Or” step. When automated, every step is executed sequentially.
Below is a bad example based on a classic Super Mario video game, showing how people might want to use “Or”:
# BAD EXAMPLE! Do not copy. Feature: SNES Mario Controls Scenario: Mario jumps Given a level is started When the player pushes the "A" button Or the player pushes the "B" button Then Mario jumps straight up
Clearly, the author’s intent is to say that Mario should jump when the player pushes either of two buttons. The author wants to cover multiple variations of the same behavior. In order to do this the right way, use Scenario Outline sections to cover multiple variations of the same behavior, as shown below:
Feature: SNES Mario Controls Scenario Outline: Mario jumps Given a level is started When the player pushes the "<letter>" button Then Mario jumps straight up Examples: Buttons | letter | | A | | B |
The Known Unknowns
Test data can be difficult to handle. Sometimes, it may be possible to seed data in the system and write tests to reference it, but other times, it may not. Google search is the prime example: the result list will change over time as both Google and the Internet change. To handle the known unknowns, write scenarios defensively so that changes in the underlying data do not cause test runs to fail. Furthermore, to be truly behavior-driven, think about data not as test data but as examples of behavior.
Consider the following example from the previous post:
Feature: Google Searching Scenario: Simple Google search Given a web browser is on the Google page When the search phrase "panda" is entered Then results for "panda" are shown And the following related results are shown | related | | Panda Express | | giant panda | | panda videos |
This scenario uses a step table to explicitly name results that should appear for a search. The step with the table would be implemented to iterate over the table entries and verify each appeared in the result list. However, what if Panda Express were to go out of business and thus no longer be ranked as high in the results? (Let’s hope not.) The test run would then fail, not because the search feature is broken, but because a hard-coded variation became invalid. It would be better to write a step that more intelligently verified that each returned result somehow related to the search phrase, like this: “And links related to ‘panda’ are shown on the results page.” The step definition implementation could use regular expression parsing to verify the presence of “panda” in each result link.
Another nice feature of Gherkin is that step definitions can hide data in the automation when it doesn’t need to be exposed. Step definitions may also pass data to future steps in the automation. For example, consider another Google search scenario:
Feature: Google Searching Scenario: Search result linking Given Google search results for "panda" are shown When the user clicks the first result link Then the page for the chosen result link is displayed
Notice how the When step does not explicitly name the value of the result link – it simply says to click the first one. The value of the first link may change over time, but there will always be a first link. The Then step must know something about the chosen link in order to successfully verify the outcome, but it can simply reference it as “the chosen result link”. Behind the scenes, in the step definitions, the When step can store the value of the chosen link in a variable and pass the variable forward to the Then step.
Handling Test Data
Some types of test data should be handled directly within the Gherkin, but other types should not. Remember that BDD is specification by example – scenarios should be descriptive of the behaviors they cover, and any data written into the Gherkin should support that descriptive nature. Read Handling Test Data in BDD for comprehensive information on handling test data.
Less is More
Scenarios should be short and sweet. I typically recommend that scenarios should have a single-digit step count (<10). Long scenarios are hard to understand, and they are often indicative of poor practices. One such problem is writing imperative steps instead of declarative steps. I have touched on this topic before, but I want to thoroughly explain it here.
Imperative steps state the mechanics of how an action should happen. They are very procedure-driven. For example, consider the following When steps for entering a Google search:
- When the user scrolls the mouse to the search bar
- And the user clicks the search bar
- And the user types the letter “p”
- And the user types the letter “a”
- And the user types the letter “n”
- And the user types the letter “d”
- And the user types the letter “a”
- And the user types the ENTER key
Now, the granularity of actions may seem like overkill, but it illustrates the point that imperative steps focus very much on how actions are taken. Thus, they often need many steps to fully accomplish the intended behavior. Furthermore, the intended behavior is not always as self-documented as with declarative steps.
Declarative steps state what action should happen without providing all of the information for how it will happen. They are behavior-driven because they express action at a higher level. All of the imperative steps in the example above could be written in one line: “When the user enters ‘panda’ at the search bar.” The scrolling and keystroking is implied, and it will ultimately be handled by the automation in the step definition. When trying to reduce step count, ask yourself if your steps can be written more declaratively.
Another reason for lengthy scenarios is scenario outline abuse. Scenario outlines make it all too easy to add unnecessary rows and columns to their Examples tables. Unnecessary rows waste test execution time. Extra columns indicate complexity. Both should be avoided. Below are questions to ask yourself when facing an oversized scenario outline:
- Does each row represent an equivalence class of variations?
- For example, searching for “elephant” in addition to “panda” does not add much test value.
- Does every combination of inputs need to be covered?
- N columns with M inputs each generates MN possible combinations.
- Consider making each input appear only once, regardless of combination.
- Do any columns represent separate behaviors?
- This may be true if columns are never referenced together in the same step.
- If so, consider splitting apart the scenario outline by column.
- Does the feature file reader need to explicitly know all of the data?
- Consider hiding some of the data in step definitions.
- Some data may be derivable from other data.
These questions are meant to be sanity checks, not hard-and-fast rules. The main point is that scenario outlines should focus on one behavior and use only the necessary variations.
Style and Structure
While style often takes a backseat during code review, it is a factor that differentiates good feature files from great feature files. In a truly behavior-driven team, non-technical stakeholders will rely upon feature files just as much as the engineers. Good writing style improves communication, and good communication skills are more than just resume fluff.
Below are a number of tidbits for good style and structure:
- Focus a feature on customer needs.
- Limit one feature per feature file. This makes it easy to find features.
- Limit the number of scenarios per feature. Nobody wants a thousand-line feature file. A good measure is a dozen scenarios per feature.
- Limit the number of steps per scenario to less than ten.
- Limit the character length of each step. Common limits are 80-120 characters.
- Use proper spelling.
- Use proper grammar.
- Capitalize Gherkin keywords.
- Capitalize the first word in titles.
- Do not capitalize words in the step phrases unless they are proper nouns.
- Do not use punctuation (specifically periods and commas) at the end of step phrases.
- Use single spaces between words.
- Indent the content beneath every section header.
- Separate features and scenarios by two blank lines.
- Separate examples tables by 1 blank line.
- Do not separate steps within a scenario by blank lines.
- Space table delimiter pipes (“|”) evenly.
- Adopt a standard set of tag names. Avoid duplicates.
- Write all tag names in lowercase, and use hyphens (“-“) to separate words.
- Limit the length of tag names.
Without these rules, you might end up with something like this:
# BAD EXAMPLE! Do not copy. Feature: Google Searching @AUTOMATE @Automated @automation @Sprint32GoogleSearchFeature Scenario outline: GOOGLE STUFF Given a Web Browser is on the Google page, when The seach phrase "<phrase>" Enter, Then "<phrase>" shown. and The relatedd results include "<related>". Examples: animals | phrase | related | | panda | Panda Express | | elephant | elephant Man |
Don’t do this. It looks horrible. Please, take pride in your profession. While the automation code may look hairy in parts, Gherkin files should look elegant.
Gherkinize Those Behaviors!
With these best practices, you can write Gherkin feature files like a pro. Don’t be afraid to try: nobody does things perfectly the first time. As a beginner, I broke many of the guidelines I put in this post, but I learned as I went. Don’t give up if you get stuck. Always remember the Golden Gherkin Rule and the Cardinal Rule of BDD!
This is the last of three posts in the series focused exclusively on Gherkin. The next post will address how to adopt behavior-driven practices into the Agile software development process.