How do you test code that depends on shared org-wide data (e.g., user settings, custom metadata)?

Some code depends on data that exists outside test isolation: User records, Profiles, Custom Metadata.

User records:

• Tests can create test users.
• System.runAs(user) to test under that user.

Profiles:

• Profile records EXIST in test context (not isolated).
• Reference profile by name: [SELECT Id FROM Profile WHERE Name = 'Standard User'].

Custom Metadata Type:

• CMDT records ARE visible in tests (treated like metadata, not data).
• No need to create in tests.

Custom Settings:

• Custom Setting records NOT visible in tests by default.
• Create in @TestSetup if needed.

Custom Permissions:

• Visible in tests (metadata).

Picklist values:

• Defined in metadata; visible in tests.

Test patterns:

@TestSetup
static void setup() {
    // For Custom Settings:
    My_Settings__c s = new My_Settings__c(Threshold__c=100);
    insert s;
}

@isTest
static void testWithCMDT() {
    // CMDT visible without setup
    My_Type__mdt config = My_Type__mdt.getInstance('Default');
    System.assertNotEquals(null, config);
}

Common pitfalls:

• Forgetting Custom Settings need explicit setup.
• Hardcoded Profile IDs (varies per org).
• Assuming all metadata visible (some isn't).

Senior insight: understand what's visible vs not in tests. Patterns vary.