src/main/java/org/fest/assertions/FileAssert.java
public @NotNull FileAssert isRelative() {
    isNotNull();
    if (!actual.isAbsolute()) {
      return this;
    }
    failIfCustomMessageIsSet();
    throw failure(format("file:<%s> should be a relative path", actual));
  }
public @NotNull FileAssert isRelative() {
    isNotNull();
    if (!actual.isAbsolute()) {
      return this;
    }
    failIfCustomMessageIsSet();
    throw failure(format("file:<%s> should be a relative path", actual));
  }
Verifies that the actual {@code File} is a relative path.

@return this assertion object.
@throws AssertionError if the actual {@code File} is not a relative path.