Added time filter to query search page (#1329)

* Added time filter to query search page

* Added start date

* Updated python endpoint test

* changed spec

* Added specs and tests

* Modified python/js tests and some function/file names
based on code review comments

* Resolved conflicts in DashboardSelect_spec and QuerySearch_spec

* Break python tests for separate functions, Move sql queries to setUp()

* Get around eslint error for spec

* Small changes based on comments

caravel/assets/spec/javascripts/sqllab/DatabaseSelect_spec.jsx

@@ -0,0 +1,34 @@
+import React from 'react';
+import Select from 'react-select';
+import DatabaseSelect from '../../../javascripts/SqlLab/components/DatabaseSelect';
+import { shallow } from 'enzyme';
+import { describe, it } from 'mocha';
+import { expect } from 'chai';
+import sinon from 'sinon';
+
+describe('DatabaseSelect', () => {
+  const mockedProps = {
+    actions: {},
+  };
+  it('is valid element', () => {
+    expect(
+      React.isValidElement(<DatabaseSelect {...mockedProps} />)
+    ).to.equal(true);
+  });
+
+  it('has one select', () => {
+    const wrapper = shallow(
+      <DatabaseSelect {...mockedProps} />
+    );
+    expect(wrapper.find(Select)).to.have.length(1);
+  });
+
+  it('calls onChange on select change', () => {
+    const onChange = sinon.spy();
+    const wrapper = shallow(
+      <DatabaseSelect onChange={onChange} />
+    );
+    wrapper.find(Select).simulate('change', { value: 1 });
+    expect(onChange).to.have.property('callCount', 1);
+  });
+});