doc(testing): Add testing section

docs/CONTRIBUTING.md

@@ -5,3 +5,67 @@
 - `main` is the main branch.
 - `beta` is the branch where the latest changes are merged into.
 - <your-github-user>/<what-you-are-gonna-change>
+
+## Testing
+
+### Monad tests
+
+From testing perspective, we are applying a role based testing approach. In this case,
+the role is monad, and we create tests cases for each monad.
+
+check the `src/monads/monads.test.ts` folder for more information.
+
+So, you have just to new test cases for your new monad that you are going to implement.
+
+
+### Matchable tests
+
+From testing perspective, we are applying a role based testing approach. In this case,
+the role is matchable, and we create tests cases for each matchable.
+
+check the `src/matchable/matchable.test.ts` folder for more information.
+
+So, you have just to new test cases for your new matchable that you are going to implement.
+
+
+### Specific tests for each monad
+
+Each `monad` has a particular way to be created or a particular API. So, we have to create
+specific tests for them.
+
+for example, the 'Try' monad has a particular way to be created, so we have to create
+tests for that.
+
+```typescript
+import { describe, it, expect } from 'vitest';
+import { Failure, Success, Try } from './try';
+
+  it.each([
+  { type: 'Success', executable: () => 2, expected: new Success(2) },
+  {
+    type: 'Failure',
+    executable: () => {
+      throw new Error();
+    },
+    expected: new Failure(new Error()),
+  },
+])('should create $type correctly', ({ executable, expected }) => {
+  expect(Try.execute(executable)).toEqual(expected);
+});
+```
+
+or the 'Option' monad has a particular API, so we have to create tests for that.
+
+```typescript
+import { describe, it, expect } from 'vitest';
+import { None, Option, Some } from './option';
+
+it.each([
+  { type: 'Some', option: Option.of(2), expected: 2 },
+  { type: 'None', option: Option.of<number>(undefined), expected: 2 },
+])('$type should handle getOrElse operation correctly', ({ option, expected }) => {
+  expect(option.getOrElse(2)).toEqual(expected);
+});
+```
+
+