Enhancement for test mechanism

[chunming-c]

@AllenFang

I have some ideas to enhance how we test. If you think it does will be better and worthy to do, I'll put it in backlog and implement in the future.

1. render components in setup function
2. all packages/react-bootstrap-table2 to be searched from the requiring module’s location

For topic 1, previously we rendered our components in each test case. As the more feature was implemented, the file will become longer and longer when the props is getting much more. I thought it will be better to extract common props and pass specific props by options for each test case.

for example:
before

describe('Cell', () => {
  describe('scenario 1', ... 
    beforeEach(() => {
      wrapper = shallow(<Cell row={ row } columnIndex={ 1 } rowIndex={ 1 } column={ column } />);
    })
  });

  describe('scenario 2', ...
    beforeEach(() => {
      wrapper = shallow(
        <Cell
          row={ row }
          rowIndex={ rowIndex }
          column={ column }
          columnIndex={ columnIndex }
          editable
          editMode={ Const.CLICK_TO_CELL_EDIT }
          onStart={ onStartCallBack }
        />
      );
  });
});

after

const props = { row, rowIndex, column, columnIndex };
const setup = options => shallow(<Cell { ...props } { ...options }/>);

describe('Cell', () => {
  describe('scenario 1' ...
    beforeEach(() => {
      wrapper = setup();
    })
  });

  describe('scenario 2', ...
    beforeEach(() => {
      wrapper = setup({
        editable: true,
        editMode: Const.CLICK_TO_CELL_EDIT,
        onStart: onStartCallBack
      })
  });
});

and
For topic 2, it will set alias for our packages.

before:
import SelectionCell from '../../src/row-selection/selection-cell';

after:
import SelectionCell from 'src/row-selection/selection-cell';

[AllenFang]

good, but I like the setup name to be shallow, enzyme have shallow, render and mount
I think the common function name(setup) can be same as the method of enzyme

@Chun-MingChen