Added prefer header tests

PreferHeader.http

@@ -0,0 +1,60 @@
+
+{{
+    const axios = require('axios');
+    
+    const wait = axios.get(`${baseUrl}/products`).then(res => {
+        let length = res.data.length;
+        let exists = res.data.find(item => item.id === 78);
+        if(length===78 && exists){
+            return axios.delete(`${baseUrl}/products?id=eq.78`)
+            .then(res => {
+                return null;
+            })
+        }
+        return null;
+    })
+    exports.wait = wait;
+}}
+###
+
+POST {{baseUrl}}/products
+Content-Type: application/json
+Prefer: return=representation
+
+{
+  "id": 78,
+  "product_name": "Saffaron",
+  "discontinued": 0,
+  "supplier_id": 12,
+  "category_id": 2,
+  "quantity_per_unit": "20 mg",
+  "unit_price": 100,
+  "units_in_stock": 50,
+  "units_on_order": 0,
+  "reorder_level": 10
+}
+?? status == 201
+?? js response.parsedBody.length == 1
+?? js response.parsedBody[0].id == 78
+?? js response.parsedBody[0].product_name == Saffaron
+
+###
+
+POST {{baseUrl}}/products
+Content-Type: application/json
+Prefer: return=headers-only
+
+{
+  "id": 78,
+  "product_name": "Saffaron",
+  "discontinued": 0,
+  "supplier_id": 12,
+  "category_id": 2,
+  "quantity_per_unit": "20 mg",
+  "unit_price": 100,
+  "units_in_stock": 50,
+  "units_on_order": 0,
+  "reorder_level": 10
+}
+?? status == 201
+?? header location == /products?id=eq.78