Update testing.mdx (#242)

* Update testing.mdx

added documentation fot api testing with cypress

* Minor edits

---------

Co-authored-by: Jan C. Brammer <[email protected]>

docs/development/testing.mdx

@@ -185,6 +185,41 @@ cy.createDefaultUser('[email protected]', 'cu1').then((user) => {
 });
 ```
 
+### Example of testing an API endpoint with Cypress
+
+You can also use Cypress to test APIs in a developer-friendly way. 
+You can conveniently access the API response data from the test runner. 
+When you click on the request step, Cypress will display the corresponding response data in the browser's console.
+
+Consider the following example, where we are testing `Collection API (GET request)`.
+
+```javascript
+cy.request('/api/v1/collections/roots.json').as('roots');
+cy.get('@roots').then(response => {
+    expect(response.status).to.eq(200);
+    const collectionData = response.body['collections'][0];
+    expect(collectionData.id).to.eq(3);
+    expect(collectionData.label).to.eq('Col1');
+});
+```
+Here, were are sending a GET request to the `api/v1/collections/roots.json` endpoint and verify that its `response.status` is `200`.
+The response body can contain objects, arrays, attributes, etc. This is how we can access a specific component from its body and perform checks on it.
+
+```javascript
+// whole object 
+const collectionData = response.body['collections'];
+
+// single item from the object list
+const collectionData = response.body['collections'][0];
+
+// check length of object
+expect(response.body['collections'].length).to.eq(0)
+
+// check if returned fields are matching exactly what's expected
+expect(collectionData.id).to.eq(3);
+expect(collectionData.label).to.eq('Col1');
+```
+
 ## General rules of thumb
 
 - All public methods should be tested, every statement, conditional branch should be covered.