By using a test-function method, we construct
n exact solutions of a quantum harmonic oscillator with a time-dependent "spring constant". Any
n-th solution describes a wave-packet train consisting of
n+1 packets. Its center oscillates like the classically harmonic oscillator with variable frequency, and width and highness of each packet change simultaneously. When the deformation is small, it behaves like a soliton train, and the large deformation is identified with collapse and revival of the wave-packet train.