Stalin fully expected Hitler to break the pact...just not while Germany was still at war with Britain.
The surviving members of Stalin’s staff in recent years say the opposite — that Stalin couldn’t believe the reports of the attacks, and took a great deal of convincing that Hitler had attacked. The most surprising part of this, IMHO, is that any of Stalin’s staff *survived* Stalin. ;’)
On the German side, in the book “Interrogations”, a high-ranking German general, captured and interrogated, told his Allied inquisitor that Hitler was constantly concerned about the reports of Soviet raids across the frontier after the division of Poland.