[explore] DatasourceControl to pick datasource in modal (#3210)

* [explore] DatasourceControl to pick datasource in modal

Makes it easier to change datasource, also makes it such that the list
of all datasources doesn't need to be loaded upfront.

* Adding more metadata

superset/assets/spec/javascripts/explore/components/DatasourceControl_spec.jsx

@@ -0,0 +1,32 @@
+import React from 'react';
+import sinon from 'sinon';
+import { expect } from 'chai';
+import { describe, it, beforeEach } from 'mocha';
+import { shallow } from 'enzyme';
+import { Modal } from 'react-bootstrap';
+import DatasourceControl from '../../../../javascripts/explore/components/controls/DatasourceControl';
+
+const defaultProps = {
+  name: 'datasource',
+  label: 'Datasource',
+  value: '1__table',
+  datasource: {
+    name: 'birth_names',
+    type: 'table',
+    uid: '1__table',
+    id: 1,
+  },
+  onChange: sinon.spy(),
+};
+
+describe('DatasourceControl', () => {
+  let wrapper;
+
+  beforeEach(() => {
+    wrapper = shallow(<DatasourceControl {...defaultProps} />);
+  });
+
+  it('renders a Modal', () => {
+    expect(wrapper.find(Modal)).to.have.lengthOf(1);
+  });
+});

superset/assets/spec/javascripts/explore/exploreActions_spec.js

@@ -82,44 +82,6 @@ describe('fetching actions', () => {
     });
   });
 
-  describe('fetchDatasources', () => {
-    const makeRequest = () => {
-      request = actions.fetchDatasources();
-      request(dispatch);
-    };
-
-    it('calls fetchDatasourcesStarted', () => {
-      makeRequest();
-      expect(dispatch.args[0][0].type).to.equal(actions.FETCH_DATASOURCES_STARTED);
-    });
-
-    it('makes the ajax request', () => {
-      makeRequest();
-      expect(ajaxStub.calledOnce).to.be.true;
-    });
-
-    it('calls correct url', () => {
-      const url = '/superset/datasources/';
-      makeRequest();
-      expect(ajaxStub.getCall(0).args[0].url).to.equal(url);
-    });
-
-    it('calls correct actions on error', () => {
-      ajaxStub.yieldsTo('error', { responseJSON: { error: 'error text' } });
-      makeRequest();
-      expect(dispatch.callCount).to.equal(2);
-      expect(dispatch.getCall(1).args[0].type).to.equal(actions.FETCH_DATASOURCES_FAILED);
-    });
-
-    it('calls correct actions on success', () => {
-      ajaxStub.yieldsTo('success', { data: '' });
-      makeRequest();
-      expect(dispatch.callCount).to.equal(3);
-      expect(dispatch.getCall(1).args[0].type).to.equal(actions.SET_DATASOURCES);
-      expect(dispatch.getCall(2).args[0].type).to.equal(actions.FETCH_DATASOURCES_SUCCEEDED);
-    });
-  });
-
   describe('fetchDashboards', () => {
     const userID = 1;
     const mockDashboardData = {