I'm admittedly more familiar with the German side of this question, but I've been trying to understand the Soviet side for a while and just can't wrap my head around it. Joseph Stalin was one of the most paranoid leaders of his time, and his executions and exiles of anyone he was suspicious of are very well-known. Surely he wouldn't have trusted the self-proclaimed "bulwark against bolshevism" to be an ally, at least not for long. But then operation Barbarossa showed that the Soviets were completely unprepared.
My question is, how much faith did Stalin really have in the non-aggression pact? It caught the Soviet Union unprepared, was that due to command decisions from higher up the chain or localized leaders being unprepared? Obviously the purges had obliterated a lot of institutional knowledge in the Soviet military, and this must have hampered their ability to respond to the invasion. Did the Soviets anticipate war with Germany at a later time, and were just not ready for it then?
Simply put, Stalin and the Soviets knew to not fully trust the non-aggression pact, but didn't anticipate a war with Germany as early as 1941.
There's a number of threads that may be of interest to you on the topic!
https://www.reddit.com/r/AskHistorians/comments/68gklq/stalin_disappeared_for_several_days_following/dgz5me1/
https://www.reddit.com/r/AskHistorians/comments/1bfxi7/did_stalin_intend_to_break_the_molotovribbentrop/
The problem with questions of the form "did Stalin think X?" is that Stalin was notoriously opaque, and archival records of the period hopelessly incomplete/fragmentary, accounts untrustworthy. Also, he was habitually insincere and duplicitous, and his actions tended to take everybody by surprise - this is a guy whose closest associates and family found impenetrable and unpredictably whimsical.
Thus anyone telling you "Stalin thought X" is automatically on shaky ground. We're making educated guesses here, one way or another.
That aside, I'm prepared to argue that Stalin did in fact expect Hitler to honour the agreement as it stood in 1941 (and happy to debate this), because he persistently discarded accurate intel, honoured and expanded the terms of their trade agreements, and took no measures to prepare a coherent defensive posture/strategy. This is not the behaviour of a man who expects to be imminently betrayed. With the wealth of evidence and warnings he had indicating the truth of the situation, his stubborn denialism demonstrates just how strongly he believed that Hitler would not act first.
His motives are, as usual, disputable. I'd posit two: firstly, his reflexive mistrust of the British - if they'd told him that Hitler was definitely not going to attack rather than giving the full scoop from ULTRA he'd probably have taken the actual threat much more seriously (speculative); secondly, he consistently overestimated Hitler's rationality and pragmatism - Hitler was an extreme gambler, utterly reckless. Barbarossa was foolish, Stalin knew this better than Hitler owing to his more accurate knowledge of Soviet strength and capability, and also a clear picture of German weakness; thus he perhaps fell victim to a delusion of Hitler as a rational actor in his own mold.
Questions of whether Stalin himself intended to honour the pact or possibly join Axis efforts against the West at a later date are open. Stalin expected general war sometime in '43-4, but the nature and cause of this war (in his view) are unclear - likely he was playing it by ear, so to speak. Seeking to exploit any opportunity as it rose - but Hitler seized the initiative, and the rest is history.
I invite more debate on this topic, as it's really the last great mystery of WWII.