Knowledge Base > IntelliJ Plugin > Covering all enum values

Covering all enum values

The Diffblue Cover Plugin for IntelliJ can write tests which ensure that all possible values of an Enum type are covered by the test suite when that Enum is passed to a method as an argument or is a return value of a method.

Enabling “Cover all enum values” behavior

This behavior is disabled by default. To enable this behavior, go in IntelliJ IDEA to File -> Settings (Windows/Linux) or IntelliJ IDEA -> Preferences (macOS), and ensure the Diffblue Cover -> Test Generation -> Cover all enum values box is checked.

Examples of tests with and without “Cover all enum values”

To understand the difference Cover all enum values makes to generated tests, we can write tests on a simple class which takes an Enum type as an argument and behaves in different ways depending upon that argument’s value.

public class ErrorFormatter {

  private static final String NON_FATAL_ERROR_TEMPLATE =
      "<p style=\"color:orange\"><em>non-fatal: %s</em></p>";

  private static final String FATAL_ERROR_TEMPLATE =
      "<p style=\"color:red\"><strong>FATAL! %s</strong></p>";

  public String asHtml(ErrorLevel level, String message) {
    switch (level) {
      case INFORMATIONAL:
      case WARNING:
        return String.format(NON_FATAL_ERROR_TEMPLATE, message);
      case FATAL:
        return String.format(FATAL_ERROR_TEMPLATE, message);
      default:
        throw new AssertionError(String.format("Unrecognised error level %s", level));
    }
  }
}

Note in particular that the method exhibits the same behavior when the level argument is INFORMATIONAL or WARNING. Two tests that exercise this method by passing those two values to its first argument will therefore cover the same lines of code.

When we write tests on this method with Cover all enum values disabled, then Diffblue Cover Plugin for IntelliJ produces these tests

@Test
public void testAsHtml() {
  assertEquals("<p style=\"color:orange\"><em>non-fatal: Not all who wander are lost</em></p>",
      (new ErrorFormatter()).asHtml(ErrorLevel.INFORMATIONAL, "Not all who wander are lost"));
  assertEquals("<p style=\"color:red\"><strong>FATAL! Not all who wander are lost</strong></p>",
      (new ErrorFormatter()).asHtml(ErrorLevel.FATAL, "Not all who wander are lost"));
}

When we enable Cover all enum values and write tests again, the Diffblue Cover Plugin for IntelliJ produces these tests

@Test
public void testAsHtml() {
  assertEquals("<p style=\"color:orange\"><em>non-fatal: Not all who wander are lost</em></p>",
      (new ErrorFormatter()).asHtml(ErrorLevel.INFORMATIONAL, "Not all who wander are lost"));
  assertEquals("<p style=\"color:orange\"><em>non-fatal: Not all who wander are lost</em></p>",
      (new ErrorFormatter()).asHtml(ErrorLevel.WARNING, "Not all who wander are lost"));
  assertEquals("<p style=\"color:red\"><strong>FATAL! Not all who wander are lost</strong></p>",
      (new ErrorFormatter()).asHtml(ErrorLevel.FATAL, "Not all who wander are lost"));
}

With Cover all enum values enabled the Diffblue Cover Plugin for IntelliJ creates an extra test, to ensure that both the INFORMATION and WARNING levels are tested even though the extra test may not increase the test suite’s measured coverage.