[Salesforce ID generator] Generates 15-character Salesforce IDs for testing #salesforce #apex

TestUtil.cls

/**
 * A collection of static utility methods for unit testing.
 */
@IsTest
public class TestUtil {

	// ID generator configuration
	private static final Integer ID_RESERVED_CHARACTERS = 7;
	private static final Integer ID_INCREMENTER_PREFIX_LENGTH = 1;
	private static final String BASE62_ALPHABET = '0123456789abcdefghijklmnopqrstuvwqyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

	// Count of generated IDs, used as an incrementer in generateId()
	private static Integer idCount = 1;


	/**
	 * Generates a Base62 string that can be used to simulate a Salesforce ID.
	 * @return A 15-character Base62 string
	 */
	public static Id generateId() {
		// Salesforce IDs are 15-character Base62 strings. The first 7 characters will be the same for all IDs in the
		// same environment, while the last 8 characters will be an incremented identifier
		// (https://salesforce.stackexchange.com/questions/1653/what-are-salesforce-ids-composed-of)
		//
		// We'll use the current user's ID to determine the appropriate environment-specific characters. We'll set a
		// number of characters following the 7th to 'Z', to make collisions with system-generated IDs unlikely. We'll
		// then use a simple incrementing pattern to generate the remaining characters.

		// Get environment-specific ID prefix from user ID
		String envPrefix = UserInfo.getUserId().substring(0, ID_RESERVED_CHARACTERS);
		String incPrefix = ''.rightPad(ID_INCREMENTER_PREFIX_LENGTH, BASE62_ALPHABET.substring(BASE62_ALPHABET.length() - 1));

		// Generate incremented value
		Integer incrementLength = (15 - ID_RESERVED_CHARACTERS - ID_INCREMENTER_PREFIX_LENGTH);
		String increment = convertBase(idCount, 62, BASE62_ALPHABET).leftPad(incrementLength, '0');

		// Increment counter and build ID
		idCount++;
		return envPrefix + incPrefix + increment;
	}

	/**
	 * Converts an integer value to a different numerical base, using a provided alphabet for representation.
	 * @param value Value to convert
	 * @param radix Numerical base to convert to
	 * @param alphabet Sequential set of characters defining the alphabet used to represent the resulting value
	 * @return The converted value
	 */
	private static String convertBase(Integer value, Integer radix, String alphabet) {
		if (radix > alphabet.length()) {
			throw new AlphabetLengthException('Length of provided alphabet must be greater or equal to radix');
		}

		// Short circuit in case of 0
		if (value == 0) {
			return '0';
		}

		// Convert input number to given base by repeatedly dividing it by base and taking remainder
		String output = '';
		while (value > 0) {
			Integer charIndex = Math.mod(value, radix);
			output = alphabet.substring(charIndex, charIndex + 1) + output;
			System.debug('output: ' + output);
			value = value / radix;
		}

		return output;
	}


	//==================================================================================================================
	// Exceptions
	//==================================================================================================================

	public class AlphabetLengthException extends Exception {}
}

TestUtilTest.cls

@IsTest
public class TestUtilTest {

	@IsTest
	private static void shouldGenerateIds() {
		Test.startTest();
		List<Id> ids = new List<Id>();
		for (Integer i = 0; i < 400; i++) {
			Id idValue = TestUtil.generateId();
			ids.add(idValue);
		}
		Test.stopTest();

		String userIdPrefix = UserInfo.getUserId().substring(0, TestUtil.RESERVED_ID_CHARACTERS);
		String incrementPrefix = ''.rightPad(TestUtil.ID_INCREMENT_PREFIX_CHARACTERS, 'Z');

		for (Integer i = 0; i < ids.size(); i++) {
			String idString = String.valueOf(ids[i]);

			// Prefix should match user ID
			System.assert(
				idString.startsWith(userIdPrefix),
				'Expected first ' + TestUtil.RESERVED_ID_CHARACTERS + ' characters of ID to match user ID: ' + idString
			);

			// Incrementing value should start with prefix
			System.assert(
				idString.substring(TestUtil.RESERVED_ID_CHARACTERS).startsWith(incrementPrefix),
				'Expected ID to contain \'' + incrementPrefix + '\': ' + idString
			);

			// last characters should increment in Base62
			Integer char1Index = Math.Mod(i, 62);
			String char1 = TestUtil.BASE62_ALPHABET.substring(char1Index, char1Index + 1);

			Integer char2Index = Math.Mod(i/62, 62);
			String char2 = TestUtil.BASE62_ALPHABET.substring(char2Index, char2Index + 1);

			Integer char3Index = Math.Mod(i/62/62, 62);
			String char3 = TestUtil.BASE62_ALPHABET.substring(char3Index, char3Index + 1);

			System.assert(
				idString.substring(0, 15).endsWith(char3 + char2 + char1),
				'Expected ID to end with \'' + char3 + char2 + char1 + '\': ' + idString
			);
		}
	}
}

private static final String BASE62_ALPHABET = '0123456789abcdefghijklmnopqrstuvwqyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

The BASE62_ALPHABET string has an extra lower case 'q' instead of an 'x'.