Japan's stock market faces a moment of truth

Japan’s stock market rally this year – including the surpassing of a 1989 high – was welcomed as one of the clearest signs that policymakers’ more-than-decade-long push to improve the efficiency of the $4 trillion economy was working. Now the Nikkei 225 and Topix indices are leading a sharp global selloff of equities. The slump will reveal how much substance is beneath the froth in the Asian count