Looking for logging into the Test Salesforce site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Test Salesforce site. After that you can login as usual with your login credentials.
https://login.salesforce.com/
https://developer.salesforce.com/forums/?id=906F00000008kVjIAI
https://success.salesforce.com/answers?id=90630000000hMc8AAE
https://help.salesforce.com/HTViewHelpDoc?id=users_login_history.htm
https://help.salesforce.com/htviewsolution?id=000175987
https://developer.salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_calls_login.htm
https://success.salesforce.com/answers?id=906300000015ABmAAM
https://success.salesforce.com/answers?id=9063A000000su4JQAQ
https://trailhead.salesforce.com/en/content/learn/projects/quickstart-app-builder/quickstart-app-builder4
https://success.salesforce.com/answers?id=9063A0000019ZXlQAM
https://help.salesforce.com/apex/HTViewSolution?id=000003910
https://help.salesforce.com/HTViewSolution?id=000181197
https://success.salesforce.com/answers?id=90630000000hTxLAAU