chore: add readme

Signed-off-by: nikolay <[email protected]>

.github/README.md

@@ -50,3 +50,19 @@ Examples:
     - postMigrationTestTags: @post-migration
 
 The testing matrix offers pretty big coverage as we can see. All options and combinations rely on us, and what's our end goal.
+
+### Opcode logger Testing
+
+In order to make opcode logger testing easier, we decided to use Besu's **debug_traceTransaction** responses as a source of truth for executed opcodes. The pipeline execution is as follows:
+- installs dependencies
+- compiles contracts
+- executes `npm run besu:start` - A helper script that starts the local Besu node, the version is hardcoded to 24.6.0 and it uses an official docker image. Exposed ports are:
+  - *8540* which is mapped to Besu's HTTP json-rpc relay
+  - *8541* which is mapped to Besu's WS json-rpc relay
+
+  All the overridden node properties as miner address, enabled and included apis including custom genesis file are defined in *utils/besu-configs/customConfigFile.toml*. A custom genesis file (defined in *utils/besu-configs/customGenesisFile.toml*) is needed because starting block number of all existing forks till now must be set to 0 when Besu's node is used as a local private testing network. Start-up accounts are included in *customGenesisFile.json* as well and they easily can be expanded with new user-defined ones.
+- executes specific tests - These tests have custom before and after methods that detect the target network, and if it is Besu, then execute **debug_traceTransaction** against Besu node and save the opcodes response into JSON file. That step doesn't gain us any coverage, it's needed to generate a source of truth when the same tests are executed against the Hedera local node.
+- starts Hedera local node
+- executes specific tests - These tests have custom before and after methods that detect the target network, and if it is Hedera, then execute **debug_traceTransaction** against Hedera local node and compare response opcodes with these generated against Besu and saved in JSON several steps above.
+
+Entire Besu's prerequisites and responses generation is required because each time a solidity's compiler version in the **hardhat.config.js** is changed, the developer, who did the update, must locally run these tests against Besu to generate a new hardcoded JSON which will be used for further comparison. That would be needed because let's get for example changes from solidity *0.8.23* and *0.8.24*. Contracts compiled with the older version will not include EIP-5656 (for `MCOPY` opcode) and EIP-1153 (for `TSTORE` and `TLOAD` opcodes) and **debug_traceTransaction** will return opcodes based on the contract's bytecode. When a solidity version is updated to *0.8.24* in **hardhat.config.js**, contracts will be precompiled and the new opcodes (from EIP-5656 and EIP-1153) will be introduced in the contracts bytecodes, so when we run the tests and compare **debug_traceTransaction** responses with the hardcoded ones (generated with contracts compiled with solidity *0.8.23*) they will differ. After using a CI as above, the solidity version update is not binding to developers and they shouldn't take extra care for new "source of truth" JSON generation.