docs: add missing rules to documentation (conventional-changelog#2428)

* docs: correct documentation for rules

- missing docs for rules:
 - body-case
 - footer-empty
 - body-empty
- add simple unit test for docs validation
- update lowerCase to lower-case

* test: improve unit test for rules

Author: armano2

@commitlint/rules/src/index.test.ts

@@ -1,4 +1,5 @@
 import path from 'path';
+import fs from 'fs';
 import globby from 'globby';
 import rules from '.';
 
@@ -13,6 +14,19 @@ test('rules export functions', () => {
 	expect(actual.every((rule) => typeof rule === 'function')).toBe(true);
 });
 
+test('all rules are present in documentation', () => {
+	const file = fs.readFileSync(
+		path.join(__dirname, '../../../docs/reference-rules.md'),
+		'utf-8'
+	);
+	const results = file
+		.split(/(\n|\r)/)
+		.filter((s) => s.startsWith('####') && !s.includes('`deprecated`'))
+		.map((s) => s.replace('#### ', ''));
+
+	expect(Object.keys(rules)).toEqual(expect.arrayContaining(results));
+});
+
 async function glob(pattern: string | string[]) {
 	const files = await globby(pattern, {
 		ignore: ['**/index.ts', '**/*.test.ts'],

docs/reference-rules.md

@@ -57,6 +57,11 @@ Rule configurations are either of type `array` residing on a key with the rule's
 - **condition**: `body` begins with blank line
 - **rule**: `always`
 
+#### body-empty
+
+- **condition**: `body` is empty
+- **rule**: `never`
+
 #### body-max-length
 
 - **condition**: `body` has `value` or less characters
@@ -87,11 +92,41 @@ Infinity
 0
 ```
 
+#### body-case
+
+- **condition**: `header` is in case `value`
+- **rule**: `always`
+- **value**
+
+```
+'lower-case'
+```
+
+- **possible values**
+
+```
+[
+  'lower-case', // default
+  'upper-case', // UPPERCASE
+  'camel-case', // camelCase
+  'kebab-case', // kebab-case
+  'pascal-case', // PascalCase
+  'sentence-case', // Sentence case
+  'snake-case', // snake_case
+  'start-case' // Start Case
+]
+```
+
 #### footer-leading-blank
 
 - **condition**: `footer` begins with blank line
 - **rule**: `always`
 
+#### footer-empty
+
+- **condition**: `footer` is empty
+- **rule**: `never`
+
 #### footer-max-length
 
 - **condition**: `footer` has `value` or less characters
@@ -129,7 +164,7 @@ Infinity
 - **value**
 
 ```
-'lowerCase'
+'lower-case'
 ```
 
 - **possible values**
@@ -198,7 +233,7 @@ Infinity
 - **value**
 
 ```
-'lowerCase'
+'lower-case'
 ```
 
 - **possible values**
@@ -248,7 +283,7 @@ Infinity
 - **value**
 
 ```
-'lowerCase'
+'lower-case'
 ```
 
 - **possible values**