Remix provides us with a watch window to observe and inspect contract variables. To use this feature, in the right panel, second tab from the left, fill in the Value input with 1 and ether:

Then make the first player join the Tontine game by pressing the join button. When it completes successfully, change the account and call the join method with zero ether, and you’ll get the following error in the messages output:

Have you noticed the send higher pension message in the output console? If you remember, this message was defined in the require function to show us the reason behind the exception: require(msg.value >= 1 ether && Tpension[msg.sender] == 0, "send higher pension");.

Press the Debug button in the console or go to the Debugger configuration tab to go through the steps!

The Solidity State section will show us that, unlike the first player, the second player wasn’t added successfully, as depicted in the following diagram:

In addition, when the debugging panel loads up, you will see a blue highlight that marks the part of the code being executed as the debugging progresses, which provides precious assistance.

Notice the existence of a warning button under the debugging buttons. Once pressed, it will rethrow the exception and jump directly to the last opcode before the exception happened: