docs: add a guide for E2E tests to run

e2e/TESTING_GUIDE.md

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+# Regular E2E tests
+
+This page lists the regular E2E tests to run when testing the network, in case of upgrade, etc..
+These snippets are aimed to be copy-pasted in the input in the E2E CI tool.
+
+## Inbounds and outbounds observation
+
+When we only want to verify the network correctly observe cross-chain transactions, simple deposits and withdraws are sufficient.
+
+The amount provided represent `0.0001` unit for coin with 18 decimals.
+
+```
+eth_deposit:100000000000000 eth_withdraw:100000000000000
+```
+
+## ERC20 observation
+
+When we want to verify the network correctly observe cross-chain transactions for ERC20 tokens.
+
+The amount is set to a small value so it can be used for most ERC20s regardless of the decimals.
+
+```
+erc20_deposit:1000 erc20_withdraw:1000
+```
+
+## Gateway basic workflow
+
+When we want to verify the gateway basic workflow, the happy path where cross-chain calls succeed.
+
+The amount is arbitrarily set to a small value, currently the tokens sent to the test contracts are lost.
+
+```
+eth_deposit_and_call:1000 eth_withdraw_and_call:1000 erc20_deposit_and_call:1000 erc20_withdraw_and_call:1000 zevm_to_evm_call evm_to_zevm_call
+```
+
+## Solana
+
+When it is necessary to test the Solana workflows, SOL and SPL tokens.
+
+```
+solana_deposit:1000 solana_withdraw:1000 solana_deposit_and_call:1000 spl_deposit:1000 spl_withdraw:1000 spl_deposit_and_call:1000 solana_deposit_and_call_revert:20000
+```
+
+## Gateway revert workflow
+
+When we want to verify the gateway revert workflow, the unhappy path where cross-chain calls fail
+
+### WithdrawAndCall
+
+The `withdrawAndCall` tests doesn't depend on the provided amount, this list can be used across all networks
+
+```
+eth_withdraw_and_call_revert:1000 eth_withdraw_and_call_revert_with_call:1000 erc20_withdraw_and_call_revert:1000 erc20_withdraw_and_call_revert_with_call:1000
+```
+
+### DepositAndCall
+
+The amount for reverting `depositAndCall` must depend on the chain as the value in the CCTX is used to pay for the revert fee.
+
+Note: these are estimated required values for mainnet based on the current gas price, the actual value might be different and fine-tuned. The values for ERC20 tests are set for USDC token.
+
+Ethereum: `0.0007ETH` and `3USDC`
+
+```
+eth_deposit_and_call_revert:700000000000000 eth_deposit_and_call_revert_with_call:700000000000000 erc20_deposit_and_call_revert:3000000 erc20_deposit_and_call_revert_with_call:3000000
+```
+
+BSC: `0.0008BNB` and `0.5USDC`
+
+```
+eth_deposit_and_call_revert:800000000000000 eth_deposit_and_call_revert_with_call:800000000000000 erc20_deposit_and_call_revert:500000 erc20_deposit_and_call_revert_with_call:500000
+```
+
+Polygon: `0.008POL` and `0.01USDC`
+
+```
+eth_deposit_and_call_revert:8000000000000000 eth_deposit_and_call_revert_with_call:8000000000000000 erc20_deposit_and_call_revert:10000 erc20_deposit_and_call_revert_with_call:10000
+```
+
+Base: `0.000005ETH` and `0.02USDC`
+
+```
+eth_deposit_and_call_revert:5000000000000 eth_deposit_and_call_revert_with_call:5000000000000 erc20_deposit_and_call_revert:20000 erc20_deposit_and_call_revert_with_call:20000
+```
+
+## Gateway arbitrary calls
+
+Arbitrary calls feature is an experimental and niche use case for now, these tests are not necessary for regular testing.
+
+```
+eth_withdraw_and_arbitrary_call:1000 erc20_withdraw_and_arbitrary_call:1000
+```