𝟓 𝐀𝐩𝐞𝐱 𝐔𝐧𝐢𝐭 𝐓𝐞𝐬𝐭 𝐭𝐢𝐩𝐬 𝐞𝐯𝐞𝐫𝐲 𝐒𝐚𝐥𝐞𝐬𝐟𝐨𝐫𝐜𝐞 𝐝𝐞𝐯 𝐬𝐡𝐨𝐮𝐥𝐝 𝐤𝐧𝐨𝐰

 𝟏. 𝐂𝐨𝐝𝐞 𝐬𝐭𝐨𝐫𝐚𝐠𝐞

You can save up to 6 MB of Apex code in each org, but test classes annotated with @isTest don’t count toward this limit.

𝟐. 𝐍𝐨 𝐬𝐞𝐩𝐚𝐫𝐚𝐭𝐞 𝐝𝐚𝐭𝐚𝐛𝐚𝐬𝐞 𝐟𝐨𝐫 𝐭𝐞𝐬𝐭𝐢𝐧𝐠

Even though test data rolls back, it still uses the same database. For objects with unique field constraints, inserting duplicates in tests can result in errors. Be careful!

𝟑. 𝐓𝐞𝐬𝐭 𝐦𝐞𝐭𝐡𝐨𝐝𝐬 𝐝𝐨𝐧’𝐭 𝐬𝐞𝐧𝐝 𝐞𝐦𝐚𝐢𝐥𝐬

No worries about accidentally spamming your users. Test methods are safe from triggering emails.

𝟒. 𝐍𝐨 𝐞𝐱𝐭𝐞𝐫𝐧𝐚𝐥 𝐜𝐚𝐥𝐥𝐨𝐮𝐭𝐬 𝐢𝐧 𝐭𝐞𝐬𝐭𝐬

Test methods can’t make callouts to external services, but you can use mock callouts to simulate API responses.

𝟓. 𝐒𝐎𝐒𝐋 𝐬𝐞𝐚𝐫𝐜𝐡𝐞𝐬

Any SOSL search in a test returns empty results by default. To ensure predictable results, 

use Test.setFixedSearchResults() to define the records you want.