I followed the steps in the test case when upgrading from bionic to cosmic and it passed. In the main.log file of the upgrade using 'do-release-upgrade -p' we can see url_downloadable is called only once and that the universe entry is still enabled.
2019-04-15 10:13:22,505 INFO Using config files '['./DistUpgrade.cfg']'
2019-04-15 10:13:22,505 INFO uname information: 'Linux clean-bionic-amd64 4.15.0-47-generic #50-Ubuntu SMP Wed Mar 13 10:44:52 UTC 2019 x86_64'
2019-04-15 10:13:22,517 INFO apt version: '1.6.10'
2019-04-15 10:13:22,517 INFO python version: '3.6.7 (default, Oct 22 2018, 11:32:17)
[GCC 8.2.0]'
2019-04-15 10:13:22,517 INFO release-upgrader version '18.10.11.6' started
...
2019-04-15 10:13:47,165 DEBUG examining: 'deb http://ubuntu.osuosl.org/ubuntu bionic main restricted multiverse'
2019-04-15 10:13:47,165 DEBUG verifySourcesListEntry: deb http://ubuntu.osuosl.org/ubuntu cosmic main restricted multiverse
2019-04-15 10:13:47,166 DEBUG url_downloadable: http://ubuntu.osuosl.org/ubuntu/dists/cosmic/Release
2019-04-15 10:13:47,166 DEBUG s='http' n='ubuntu.osuosl.org' p='/ubuntu/dists/cosmic/Release' q='' f=''
2019-04-15 10:13:47,330 DEBUG entry 'deb http://ubuntu.osuosl.org/ubuntu cosmic main restricted multiverse' updated to new dist
2019-04-15 10:13:47,331 DEBUG examining: 'deb http://ubuntu.osuosl.org/ubuntu bionic-updates main restricted multiverse'
2019-04-15 10:13:47,331 DEBUG entry 'deb http://ubuntu.osuosl.org/ubuntu cosmic-updates main restricted multiverse' updated to new dist
2019-04-15 10:13:47,331 DEBUG examining: 'deb http://ubuntu.osuosl.org/ubuntu bionic-security main restricted multiverse'
2019-04-15 10:13:47,332 DEBUG entry 'deb http://ubuntu.osuosl.org/ubuntu cosmic-security main restricted multiverse' updated to new dist
2019-04-15 10:13:47,332 DEBUG examining: 'deb http://ubuntu.osuosl.org/ubuntu bionic universe'
2019-04-15 10:13:47,332 DEBUG entry 'deb http://ubuntu.osuosl.org/ubuntu cosmic universe' updated to new dist
Setting to verification-done for bionic and cosmic.
I followed the steps in the test case when upgrading from bionic to cosmic and it passed. In the main.log file of the upgrade using 'do-release-upgrade -p' we can see url_downloadable is called only once and that the universe entry is still enabled.
2019-04-15 10:13:22,505 INFO Using config files '['./DistUpgrad e.cfg'] ' ubuntu. osuosl. org/ubuntu bionic main restricted multiverse' stEntry: deb http:// ubuntu. osuosl. org/ubuntu cosmic main restricted multiverse ubuntu. osuosl. org/ubuntu/ dists/cosmic/ Release osuosl. org' p='/ubuntu/ dists/cosmic/ Release' q='' f='' ubuntu. osuosl. org/ubuntu cosmic main restricted multiverse' updated to new dist ubuntu. osuosl. org/ubuntu bionic-updates main restricted multiverse' ubuntu. osuosl. org/ubuntu cosmic-updates main restricted multiverse' updated to new dist ubuntu. osuosl. org/ubuntu bionic-security main restricted multiverse' ubuntu. osuosl. org/ubuntu cosmic-security main restricted multiverse' updated to new dist ubuntu. osuosl. org/ubuntu bionic universe' ubuntu. osuosl. org/ubuntu cosmic universe' updated to new dist
2019-04-15 10:13:22,505 INFO uname information: 'Linux clean-bionic-amd64 4.15.0-47-generic #50-Ubuntu SMP Wed Mar 13 10:44:52 UTC 2019 x86_64'
2019-04-15 10:13:22,517 INFO apt version: '1.6.10'
2019-04-15 10:13:22,517 INFO python version: '3.6.7 (default, Oct 22 2018, 11:32:17)
[GCC 8.2.0]'
2019-04-15 10:13:22,517 INFO release-upgrader version '18.10.11.6' started
...
2019-04-15 10:13:47,165 DEBUG examining: 'deb http://
2019-04-15 10:13:47,165 DEBUG verifySourcesLi
2019-04-15 10:13:47,166 DEBUG url_downloadable: http://
2019-04-15 10:13:47,166 DEBUG s='http' n='ubuntu.
2019-04-15 10:13:47,330 DEBUG entry 'deb http://
2019-04-15 10:13:47,331 DEBUG examining: 'deb http://
2019-04-15 10:13:47,331 DEBUG entry 'deb http://
2019-04-15 10:13:47,331 DEBUG examining: 'deb http://
2019-04-15 10:13:47,332 DEBUG entry 'deb http://
2019-04-15 10:13:47,332 DEBUG examining: 'deb http://
2019-04-15 10:13:47,332 DEBUG entry 'deb http://
Setting to verification-done for bionic and cosmic.