Add unique-examples rule (#69)

* add unique-examples rule

* add unique-examples rule

src/rules/README.md

@@ -37,6 +37,7 @@ option.
 | [No Inconsistent Quotes](#no-inconsistent-quotes)       | `no-inconsistent-quotes`    |    ✅    |
 | [Filename Snake Case](#filename-snake-case)             | `filename-snake-case`       |    ❌    |
 | [Filename Kebab Case](#filename-kebab-case)             | `filename-kebab-case`       |    ❌    |
+| [Unique Examples](#unique-examples)                     | `unique-examples`           |    ❌    |
 
 ### Allowed Tags
 
@@ -682,3 +683,29 @@ export default {
   }
 }
 ```
+
+### Unique Examples
+
+Examples should have a unique name if there are more than 1 in a scenario outline.
+
+**Examples**
+
+Enable the rule
+
+```typescript
+export default {
+  rules: {
+    'unique-examples': 'on',
+  }
+}
+```
+
+Enable the rule and set severity
+
+```typescript
+export default {
+  rules: {
+    'unique-examples': 'error',
+  }
+}
+```

src/rules/unique-examples.ts

@@ -0,0 +1,43 @@
+import { switchOrSeveritySchema } from '../schemas'
+import Schema from '../schema'
+import Rule from '../rule'
+import { RawSchema, AcceptedSchema } from '../types'
+import Document from '../document'
+
+export default class UniqueExamples implements Rule {
+  public readonly name: string = 'unique-examples'
+
+  public readonly acceptedSchema: AcceptedSchema = switchOrSeveritySchema
+
+  public readonly schema: Schema
+
+  public constructor(rawSchema: RawSchema) {
+    this.schema = new Schema(rawSchema)
+  }
+
+  public async run(document: Document): Promise<void> {
+    document.feature.children.forEach((child) => {
+      if (!child.scenario) {
+        return
+      }
+
+      if (child.scenario.keyword !== 'Scenario Outline') {
+        return
+      }
+
+      if (!child.scenario.examples.length) {
+        return
+      }
+
+      const names = []
+      child.scenario.examples.map((e) => {
+        if (!names.includes(e.name)) {
+          names.push(e.name)
+          return
+        }
+
+        document.addError(this.name, 'Examples should contain a unique name if there are more than one.', e.location)
+      })
+    })
+  }
+}

tests/acceptance/features/unique-examples.feature

@@ -0,0 +1,42 @@
+Feature: Unique Examples
+
+  Scenario: Invalid Examples
+    Given the following feature file
+      """
+      Feature: Invalid
+        Scenario Outline:
+          Given I do <THING>
+          Then I should have done <THING>
+        Examples:
+          | THING |
+          | Swim  |
+        Examples:
+          | THING |
+          | Eat   |
+      """
+    When Gherklin is ran with the following configuration
+      | rules                        |
+      | {"unique-examples": "error"} |
+    Then there is 1 file with errors
+    And the errors are
+      | location                 | severity | rule            | message                                                           |
+      | {"line": 8, "column": 3} | error    | unique-examples | Examples should contain a unique name if there are more than one. |
+
+  Scenario: Valid Examples
+    Given the following feature file
+      """
+      Feature: Valid
+        Scenario Outline:
+          Given I do <THING>
+          Then I should have done <THING>
+        Examples: Recreational
+          | THING |
+          | Swim  |
+        Examples: Mandatory
+          | THING |
+          | Eat   |
+      """
+    When Gherklin is ran with the following configuration
+      | rules                        |
+      | {"unique-examples": "error"} |
+    Then there are 0 files with errors