Question

I need a JUnit test for this:

/**Shifts the column down by shift blocks, and fills in the top of the column with grey blocks.
*/
private void shift(){
//Stores the location of the topmost non grey block in the current column.
int columnTop = 0;

//Runs until the top most non grey block in the column is reached, and then stores that value to the field columnTop. It requires that the current button is not at the top of the column.
while((grid[columnTop][currentButtonWidth].getBackground() == Color.gray)){
columnTop = columnTop + 1;
}

//Shifts the colors down to cover the contiguous blocks. This requires that the bottom most button of the same color as the clicked button is not above the topmost colored block.
while(bottomButtonHeight >= columnTop){
grid[bottomButtonHeight][currentButtonWidth].setBackground(grid[currentButtonHeight-verticalShift][currentButtonWidth].getBackground());
bottomButtonHeight = bottomButtonHeight + 1;  
}   
}