[sqllab] fix data grid's instant search function (#4717)

* [sqllab] fix data grid's instant search function

It looks like any non-string type would break the search feature.
of `FilterableTable`

* Addressing comments

superset/assets/spec/javascripts/components/FilterableTable/FilterableTable_spec.jsx

@@ -1,15 +1,43 @@
 import React from 'react';
 import { describe, it } from 'mocha';
 import { expect } from 'chai';
+import { mount } from 'enzyme';
 import FilterableTable from '../../../../javascripts/components/FilterableTable/FilterableTable';
 
 describe('FilterableTable', () => {
   const mockedProps = {
-    orderedColumnKeys: [],
-    data: [],
-    height: 0,
+    orderedColumnKeys: ['a', 'b', 'c'],
+    data: [
+      { a: 'a1', b: 'b1', c: 'c1', d: 0 },
+      { a: 'a2', b: 'b2', c: 'c2', d: 100 },
+    ],
+    height: 500,
   };
+  let wrapper;
+  beforeEach(() => {
+    wrapper = mount(<FilterableTable {...mockedProps} />);
+  });
   it('is valid element', () => {
     expect(React.isValidElement(<FilterableTable {...mockedProps} />)).to.equal(true);
   });
+  it('renders a grid with 2 rows', () => {
+    expect(wrapper.find('.ReactVirtualized__Grid')).to.have.length(1);
+    expect(wrapper.find('.ReactVirtualized__Table__row')).to.have.length(2);
+  });
+  it('filters on a string', () => {
+    const props = {
+      ...mockedProps,
+      filterText: 'b1',
+    };
+    wrapper = mount(<FilterableTable {...props} />);
+    expect(wrapper.find('.ReactVirtualized__Table__row')).to.have.length(1);
+  });
+  it('filters on a number', () => {
+    const props = {
+      ...mockedProps,
+      filterText: '100',
+    };
+    wrapper = mount(<FilterableTable {...props} />);
+    expect(wrapper.find('.ReactVirtualized__Table__row')).to.have.length(1);
+  });
 });