Lesson 9 unit test checkUpKeep Function

[Viva903]

Hello community,

    I am failing this unit test on Lesson 9: Hardhat Smart Contract Lottery for "checkUpkeep" function. The problem is resolved when I decrease "evm_increaseTime" from 29 (30 - 1), to 28 (30 -2), but i do not understand why. Appreciate if anyone can help me to understand it.

Below is the test :

      describe("checkUpkeep", function () {
          it("returns false if enough time hasn't passed", async () => {
              await raffle.enterRaffle({ value: raffleEntranceFee })
              await network.provider.send("evm_increaseTime", [interval.toNumber() - **1**])
              await network.provider.request({ method: "evm_mine", params: [] })
              const { upkeepNeeded } = await raffle.callStatic.checkUpkeep("0x") // upkeepNeeded = (timePassed && isOpen && hasBalance && hasPlayers)
              assert(!upkeepNeeded)
          })
      })

Modified line to pass the test => await network.provider.send("evm_increaseTime", [interval.toNumber() - 2])

Thanks !