The Evolution of Public Testnets: Perspectives from Ethereum and Bitcoin

Ethereum and Bitcoin, as the two major mainstream blockchain networks, have their Testnet development history reflecting the challenges and breakthroughs in public infrastructure construction. This article will review the evolution of Ethereum and Bitcoin's Testnets, explore the technical considerations and value orientations behind them, and analyze the attributes of Testnets from the perspective of public goods economics.

The Development History of the Ethereum Testnet

Pioneer Era: Olympic and Morden

Ethereum's first public test platform, Olympic, was launched in early 2015, even before the Ethereum mainnet went live. The Olympic Testnet played an important role in early Ethereum development, but it also had issues such as a large state set and potential private key vulnerabilities.

The Morden Testnet was subsequently launched in sync with the Ethereum mainnet in July 2015. However, due to a conflict between the nonce rules and EIP-161, Morden ultimately experienced a consensus divergence at block 1885074 and was deprecated.

Ropsten Era and Security Challenges

The Ropsten Testnet was launched in November 2016, using a proof-of-work mechanism. In February 2017, Ropsten suffered a severe denial-of-service attack, and the block gas limit was raised to 9 billion. With the community's efforts, Ropsten successfully resumed operation in March 2017.

On June 8, 2022, Ropsten completed the merge from PoW to PoS, becoming the first major Testnet to complete the merge.

Authority Proof ( PoA ) Revolution

After the Ropsten attack in February 2017, it promoted the development of the authority proof ( PoA ) Testnet. The Kovan Testnet was launched in March 2017, implementing PoA consensus using the Aura algorithm.

The Rinkeby Testnet was launched in April 2017, implementing the Clique authority proof engine, aiming to provide a more general PoA solution.

Multi-client breakthrough: Goerli

The Goerli Testnet originated from the ETHBerlin hackathon in September 2018, aiming to achieve true multi-client compatibility. Goerli officially launched on January 31, 2019, supporting mainstream clients such as Geth, Parity, and Nethermind.

On August 11, 2022, Goerli successfully completed its merger with the Prater beacon chain, transitioning from PoA to PoS consensus.

Modern Testnet: Sepolia/Holešky and Hoodi

Sepolia, as a PoA Testnet, is primarily maintained by the ETHPandaOps team, focusing on execution layer testing. Holešky and Hoodi are mainly used for protocol layer testing, especially related to PoS functionalities.

Currently, Sepolia is the preferred Testnet for smart contract development, while Hoodi is the best choice for protocol layer testing.

Value Orientation of Bitcoin Testnet

There have been four major Testnets in the history of Bitcoin, named Testnet1, Testnet2, and so on. The code for Testnet3 has vulnerabilities that may cause the block difficulty to reset.

In April 2024, developer lopp attacked testnet3 to express the view that the BTC on the Testnet should not have value. This attack significantly increased the block generation speed of testnet3, impacting projects that relied on testnet3.

Finally, Bitcoin Core v28.0 added support for testnet4. Bitcoin also has other types of testnets such as Bitcoin Regtest and Bitcoin Signet.

Public Goods and Isolation Theory

The Testnet, as a public good, has the characteristic of being shared by multiple users without interfering with others' usage. To achieve optimal economic benefits, public goods are often chosen to be freely accessible.

Isolation theory provides a method for charging a portion of the fees while maintaining public accessibility. Both the Ethereum and Bitcoin Testnets adopt isolation measures and take special actions for users with a high demand for test tokens.

Overall, the evolution of the Testnet reflects the technical challenges and value trade-offs in the construction of blockchain infrastructure. Through continuous iteration and innovation, the Testnet provides important support for the development of the blockchain ecosystem.