fix proof integration test

there were two logic errors in this test:
- a slot is freed anyway at the end of the contract
- when starting the request takes a long time, the
  first slot can already be freed because there were
  too many missing proofs

tests/integration/testproofs.nim

@@ -158,8 +158,7 @@ marketplacesuite "Simulate invalid proofs":
   ):
     let client0 = clients()[0].client
     let expiry = 5.periods
-    # In 2 periods you cannot have enough invalid proofs submitted:
+    let duration = expiry + 10.periods
-    let duration = expiry + 2.periods
 
     let data = await RandomChunker.example(blocks=8)
     createAvailabilities(data.len * 2, duration) # TODO: better value for data.len
@@ -176,20 +175,27 @@ marketplacesuite "Simulate invalid proofs":
     )
     let requestId = client0.requestId(purchaseId).get
 
-    check eventually(client0.purchaseStateIs(purchaseId, "started"), timeout = expiry.int * 1000)
+    var slotWasFilled = false
+    proc onSlotFilled(event: SlotFilled) =
+      if event.requestId == requestId:
+        slotWasFilled = true
+    let filledSubscription = await marketplace.subscribe(SlotFilled, onSlotFilled)
+
+    # wait for the first slot to be filled
+    check eventually(slotWasFilled, timeout = expiry.int * 1000)
 
     var slotWasFreed = false
     proc onSlotFreed(event: SlotFreed) =
       if event.requestId == requestId:
         slotWasFreed = true
+    let freedSubscription = await marketplace.subscribe(SlotFreed, onSlotFreed)
 
-    let subscription = await marketplace.subscribe(SlotFreed, onSlotFreed)
+    # In 2 periods you cannot have enough invalid proofs submitted:
-
+    await sleepAsync(2.periods.int.seconds)
-    # check not freed
-    await sleepAsync((duration - expiry).int.seconds)
     check not slotWasFreed
 
-    await subscription.unsubscribe()
+    await filledSubscription.unsubscribe()
+    await freedSubscription.unsubscribe()
 
   # TODO: uncomment once fixed
   # test "host that submits invalid proofs is paid out less", NodeConfigs(