For years, Ethereum developers have promised a huge upgrade that would, among other things, dramatically decrease the amount of energy used by the blockchain and make it eco-friendly. On Monday, developers began a test for that upgrade, reporting that it went well, although it had some “minor issues.”

The test was a dress rehearsal for what’s called the “merge,” which aims to dramatically shift how transactions are validated on the blockchain.

The timeline for the real merge hasn’t been confirmed yet. After its next test, set for April 22, developers will have a better understanding for when it may happen. Ethereum developer Tim Beiko predicts that the merge will happen in July, although he’s said that’s a “rough estimation.”

Though the real merge is still months away, the test on Monday morning shows that it is possible, and one developer went as far as to call it a “historical event.”

What is changing for Ethereum post-merge 

The main point of the merge is switching from a proof-of-work model to a proof-of-stake model.

Ethereum currently relies on proof of work, under which crypto miners must complete complex puzzles to validate transactions. This process requires a huge amount of computer power and is often criticized due to its environmental impact.

With the planned upgrade to proof of stake, users would be able to validate transactions according to how many coins they contribute, or stake, to the network. In return for staking more coins, users have a higher likelihood of being chosen to validate transactions on the network and earn a reward.

Currently, Ethereum has both proof-of-work and proof-of-stake chains running in parallel. While both have validators, only the proof-of-work chain currently processes users’ transactions.

Once the real merge is complete, Ethereum's blockchain will shift fully to the proof-of-stake chain, called the Beacon Chain.

After the real merge, Ethereum’s crypto mining would become obsolete, which would substantially reduce its environmental impact. The supply of new Ether would also likely decline in the future, because fewer coins are expected to be issued. Additionally, blockchain security against potential attack is supposed to improve. And institutional investment in the Ethereum network is expected to increase.

How did the test go? 

To test the merge on Monday, developers attempted what’s called a “shadow fork.”

With it, they are able to re-create what would happen during the merge, without impacting the Ethereum “mainnet,” or main blockchain network. In doing this, developers had launched a small number of nodes and ran them through the merge. Nodes are computers that run software to verify transactions on the Ethereum network.

Since it’s just a few nodes running through the test, “the main Ethereum network keeps going along as if nothing happened,” Beiko told Fortune. This is useful for developers to see whether there would be any issues with the merge before impacting the entire network.

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So far, the test has been working, aside from a few “seemingly minor issues” developers are looking into.

On April 22, Ethereum developers plan to test the merge again, and until then, they’re expecting to run other smaller tests to learn more about what can be improved.  

Though many might be impatient, as the merge has been delayed multiple times in the past, David Lawant, director of research at Bitwise Asset Management, says that the various tests are necessary.

A lot of investment relies on Ethereum. It not only powers Ether, the second-largest cryptocurrency, but also supports popular decentralized finance (DeFi) applications and non-fungible tokens (NFTs).

“This is a significant engineering undertaking,” Lawant previously told Fortune. “[A] lot of testing and preparation goes into such endeavors. The mantra for such mission-critical upgrades usually is, ‘It will happen when it’s ready.’”

This story was originally featured on Fortune.com