fix(docs): prefer-expect-assertions rule docs (#49)

* docs: updating docs for prefer-expect-assertions rule

* style: minnor formating in prefer-expect-assertions doc

* docs: tweaks

Author: tushardhole

README.md

@@ -78,16 +78,17 @@ for more information about extending configuration files.
 
 ## Rules
 
-| Rule                                                           | Description                   | Recommended                                                             | Fixable                                                     |
-| -------------------------------------------------------------- | ----------------------------- | ----------------------------------------------------------------------- | ----------------------------------------------------------- |
-| [no-disabled-tests](docs/rules/no-disabled-tests.md)           | Disallow disabled tests       | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) |                                                             |
-| [no-focused-tests](docs/rules/no-focused-tests.md)             | Disallow focused tests        | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) |                                                             |
-| [no-identical-title](docs/rules/no-identical-title.md)         | Disallow identical titles     | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) |                                                             |
-| [no-large-snapshots](docs/rules/no-large-snapshots.md)         | Disallow large snapshots      |                                                                         |                                                             |
-| [prefer-to-have-length](docs/rules/prefer-to-have-length.md)   | Suggest using toHaveLength()  | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) | ![fixable](https://img.shields.io/badge/-fixable-green.svg) |
-| [prefer-to-be-null](docs/rules/prefer-to-be-null.md)           | Suggest using toBeNull()      |                                                                         | ![fixable](https://img.shields.io/badge/-fixable-green.svg) |
-| [prefer-to-be-undefined](docs/rules/prefer-to-be-undefined.md) | Suggest using toBeUndefined() |                                                                         | ![fixable](https://img.shields.io/badge/-fixable-green.svg) |
-| [valid-expect](docs/rules/valid-expect.md)                     | Enforce valid expect() usage  | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) |                                                             |
+| Rule                                                               | Description                                                     | Recommended                                                             | Fixable                                                     |
+| ------------------------------------------------------------------ | --------------------------------------------------------------- | ----------------------------------------------------------------------- | ----------------------------------------------------------- |
+| [no-disabled-tests](docs/rules/no-disabled-tests.md)               | Disallow disabled tests                                         | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) |                                                             |
+| [no-focused-tests](docs/rules/no-focused-tests.md)                 | Disallow focused tests                                          | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) |                                                             |
+| [no-identical-title](docs/rules/no-identical-title.md)             | Disallow identical titles                                       | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) |                                                             |
+| [no-large-snapshots](docs/rules/no-large-snapshots.md)             | Disallow large snapshots                                        |                                                                         |                                                             |
+| [prefer-to-have-length](docs/rules/prefer-to-have-length.md)       | Suggest using `toHaveLength()`                                  | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) | ![fixable](https://img.shields.io/badge/-fixable-green.svg) |
+| [prefer-to-be-null](docs/rules/prefer-to-be-null.md)               | Suggest using `toBeNull()`                                      |                                                                         | ![fixable](https://img.shields.io/badge/-fixable-green.svg) |
+| [prefer-to-be-undefined](docs/rules/prefer-to-be-undefined.md)     | Suggest using `toBeUndefined()`                                 |                                                                         | ![fixable](https://img.shields.io/badge/-fixable-green.svg) |
+| [prefer-expect-assertions](docs/rules/prefer-expect-assertions.md) | Suggest using `expect.assertions()` OR `expect.hasAssertions()` |                                                                         |                                                             |
+| [valid-expect](docs/rules/valid-expect.md)                         | Enforce valid `expect()` usage                                  | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) |                                                             |
 
 ## Credit
 

docs/rules/prefer-expect-assertions.md

@@ -0,0 +1,57 @@
+# Suggest using `expect.assertions()` OR `expect.hasAssertions()` (prefer-expect-assertions)
+
+Ensure every test to have either `expect.assertions(<number of assertions>)` OR
+`expect.hasAssertions()` as its first expression.
+
+## Rule details
+
+This rule triggers a warning if,
+
+* `expect.assertions(<number of assertions>)` OR `expect.hasAssertions()` is not
+  present as first statement in a test, e.g.:
+
+```js
+test('my test', () => {
+  expect(someThing()).toEqual('foo');
+});
+```
+
+* `expect.assertions(<number of assertions>)` is the first statement in a test
+  where argument passed to `expect.assertions(<number of assertions>)` is not a
+  valid number, e.g.:
+
+```js
+test('my test', () => {
+  expect.assertions('1');
+  expect(someThing()).toEqual('foo');
+});
+```
+
+### Default configuration
+
+The following patterns are considered warnings:
+
+```js
+test("my test", () => {
+  expect.assertions("1");
+  expect(someThing()).toEqual("foo");
+});
+
+test("my test", () => {
+  expect.(someThing()).toEqual("foo");
+});
+```
+
+The following patterns would not be considered warnings:
+
+```js
+test('my test', () => {
+  expect.assertions(1);
+  expect(someThing()).toEqual('foo');
+});
+
+test('my test', () => {
+  expect.hasAssertions();
+  expect(someThing()).toEqual('foo');
+});
+```