[CBR-503] Document OBFT update testing; update Changelog

Author: Michael Hueschen

CHANGELOG.md

@@ -12,7 +12,7 @@
 ### Features
 
 - Support for (unused) addresses batch import ([CO-448](https://iohk.myjetbrains.com/youtrack/issue/CO-448) [#4040](https://github.com/input-output-hk/cardano-sl/pull/4040))
-- Add `script-runner` tool to automate cluster-level testing ([DEVOPS-1131](https://iohk.myjetbrains.com/youtrack/v2/issue/devops-1131): [#3916](https://github.com/input-output-hk/cardano-sl/pull/3916) [#4057](https://github.com/input-output-hk/cardano-sl/pull/4057))
+- Add `script-runner` tool to automate cluster-level testing ([DEVOPS-1131](https://iohk.myjetbrains.com/youtrack/v2/issue/devops-1131): [#3916](https://github.com/input-output-hk/cardano-sl/pull/3916) [#4057](https://github.com/input-output-hk/cardano-sl/pull/4057) [#4061](https://github.com/input-output-hk/cardano-sl/pull/4061))
 
 - Node Monitoring API: nodes now serve their own settings and info via a web server via a `/api/v1/node-settings` and `/api/v1/node-info` (still proxied by the wallet backend) ([#110](https://github.com/input-output-hk/cardano-wallet/issues/110))
   - Set up scaffolding for node API [#3788](https://github.com/input-output-hk/cardano-sl/pull/3788)

script-runner/README.md

@@ -5,3 +5,23 @@ This module contains scripts to perform tests at the cluster level - running clu
 ### Usage
 
 See the `stack-gui` and `stack-test` scripts which contain usage commands.
+
+### Testing OBFT
+
+`script-runner` launches nodes using the `dev:` key of `lib/configuration.yaml`. We can start in OBFT era by applying a patch such as
+```
+diff --git a/lib/configuration.yaml b/lib/configuration.yaml
+index b55039730b..f67e581929 100644
+--- a/lib/configuration.yaml
++++ b/lib/configuration.yaml
+@@ -48,7 +48,7 @@ dev: &dev
+             txSizeLinear:
+               a: 155381 # absolute minimal fees per transaction
+               b: 43.946 # additional minimal fees per byte of transaction size
+-          unlockStakeEpoch: 18446744073709551615 # last epoch (maxBound @Word64)
++          unlockStakeEpoch: 9999999999999999999
+         protocolConstants: &dev_core_genesis_spec_protocolConstants
+           k: 2
+           protocolMagic: 55550001
+```
+and then running a test e.g. `cd script-runner && ./stack-test test4.1` which ensures that we can issue update proposals and see them adopted in OBFT era.