src/main/java/org/fest/assertions/internal/Files.java
public void assertIsDirectory(Description description, File actual) {
    assertNotNull(description, actual);
    if (!actual.isDirectory()) {
      String format = "expecting path:<%s> to represent an existing directory";
      throw failures.failure(description, new BasicErrorMessageFactory(format, actual));
    }
  }
public void assertIsDirectory(Description description, File actual) {
    assertNotNull(description, actual);
    if (!actual.isDirectory()) {
      String format = "expecting path:<%s> to represent an existing directory";
      throw failures.failure(description, new BasicErrorMessageFactory(format, actual));
    }
  }
Asserts that the <em>actual</em> {@code File} represents an existing directory.

@param description the description of the <em>actual</em> {@code File}.
@param actual the <em>actual</em> {@code File}.
@throws AssertionError if the <em>actual</em> {@code File} is {@code null}.
@throws AssertionError if the <em>actual</em> {@code File} does not represent an existing directory.