Testing Triggers, Classes, Controllers and Flows

What it is

Apex unit tests are methods that run your code and assert that it behaves as expected. Salesforce requires tests to deploy Apex to production: at least 75% overall code coverage, every trigger with some coverage, and every test passing.

Tests run in isolation. They create their own data, and everything they write is rolled back when the test ends.

How it works

A test class

@IsTest
private class ContactTriggerTest {
    @TestSetup
    static void makeData() {
        insert new Account(Name = 'Acme');
    }
    @IsTest
    static void setsDescriptionInBulk() {
        Account a = [SELECT Id FROM Account LIMIT 1];
        List<Contact> cs = new List<Contact>();
        for (Integer i = 0; i < 200; i++) {
            cs.add(new Contact(LastName = 'C' + i, AccountId = a.Id));
        }
        Test.startTest();
        insert cs;
        Test.stopTest();
        for (Contact c : [SELECT Description FROM Contact]) {
            Assert.areEqual('Acme', c.Description);
        }
    }
}

Key features

By default, tests cannot see existing org data (except some setup data such as users and profiles). A query for Accounts in a test with no setup returns nothing.

Testing different code

Test data factory

A public @IsTest utility class with static methods such as createAccounts(Integer n) gives every test consistent, valid data and keeps setup in one place.

Coverage arithmetic

Coverage counts executable lines only; comments and blank lines are ignored. If a class has 70 executable lines and tests run 56 of them, coverage is 80%.

A worked example

A trigger rejects contacts without Email using addError(). A good test inserts 200 contacts with Database.insert(contacts, false), three without Email. It checks that the three SaveResult entries failed with the trigger's message, and that 197 contacts exist afterwards. That one test proves bulk behaviour, the rejection path and the message, which coverage alone never shows.

How the exam asks about this

• "Async code must finish before the assertions." Wrap it in Test.startTest() and Test.stopTest().
• "Test that a user without access sees no records." System.runAs().
• "Code makes a callout." Test.setMock with an HttpCalloutMock.