[Enhancement] Fetch previous messages in the conversation (#355)

* Fetch previous messages in the conversation

* Add specs for conversation store

* Fix codeclimate issues

* Exclude specs folder

* Exclude globally

* Fix path in exclude patterns

* Add endPoints spec

* Add snapshots for Spinner

* Add specs for actions

app/javascript/widget/api/specs/endPoints.spec.js

@@ -0,0 +1,25 @@
+import endPoints from '../endPoints';
+
+describe('#sendMessage', () => {
+  it('returns correct payload', () => {
+    expect(endPoints.sendMessage('hello')).toEqual({
+      url: `/api/v1/widget/messages`,
+      params: {
+        message: {
+          content: 'hello',
+        },
+      },
+    });
+  });
+});
+
+describe('#getConversation', () => {
+  it('returns correct payload', () => {
+    expect(endPoints.getConversation({ before: 123 })).toEqual({
+      url: `/api/v1/widget/messages`,
+      params: {
+        before: 123,
+      },
+    });
+  });
+});