test: move releases download incantation to README

Author: Sjors

test/README.md

@@ -84,6 +84,12 @@ Run all possible tests with
 test/functional/test_runner.py --extended
 ```
 
+In order to run backwards compatibility tests, download the previous node binaries:
+
+```
+test/get_previous_releases.py -b v0.20.1 v0.19.1 v0.18.1 v0.17.2 v0.16.3 v0.15.2
+```
+
 By default, up to 4 tests will be run in parallel by test_runner. To specify
 how many jobs to run, append `--jobs=n`
 

test/functional/feature_backwards_compatibility.py

@@ -4,9 +4,8 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Backwards compatibility functional test
 
-Test various backwards compatibility scenarios. Download the previous node binaries:
-
-test/get_previous_releases.py -b v0.20.1 v0.19.1 v0.18.1 v0.17.2 v0.16.3 v0.15.2
+Test various backwards compatibility scenarios. Requires previous releases binaries,
+see test/README.md.
 
 v0.15.2 is not required by this test, but it is used in wallet_upgradewallet.py.
 Due to a hardfork in regtest, it can't be used to sync nodes.

test/functional/mempool_compatibility.py

@@ -7,10 +7,7 @@
 NOTE: The test is designed to prevent cases when compatibility is broken accidentally.
 In case we need to break mempool compatibility we can continue to use the test by just bumping the version number.
 
-Download node binaries:
-test/get_previous_releases.py -b v0.20.1 v0.19.1 v0.18.1 v0.17.2 v0.16.3 v0.15.2
-
-Only v0.15.2 is required by this test. The rest is used in other backwards compatibility tests.
+The previous release v0.15.2 is required by this test, see test/README.md.
 """
 
 import os

test/functional/wallet_upgradewallet.py

@@ -6,9 +6,8 @@
 
 Test upgradewallet RPC. Download node binaries:
 
-test/get_previous_releases.py -b v0.20.1 v0.19.1 v0.18.1 v0.17.2 v0.16.3 v0.15.2
-
-Only v0.15.2 and v0.16.3 are required by this test. The others are used in feature_backwards_compatibility.py
+Requires previous releases binaries, see test/README.md.
+Only v0.15.2 and v0.16.3 are required by this test.
 """
 
 import os