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

@return this assertion object.
@throws AssertionError if the the actual {@code File} is {@code null}.
@throws AssertionError if the actual {@code File} is not a regular file.