function testStatistic( x, m ) {
	var i;
	for ( i = 0; i < x.length; i++ ) {
		x[ i ] = ( x[i]*x[i] ) / m[ i ];
	}
	return dsumpw( x.length, x, 1 );
}
Computes the test statistic.

## Notes

-   Mutates the first input array.

@private
@param {Float64Array} x - absolute differences
@param {Float64Array} m - expected frequencies
@returns {number} test statistic