src/main/java/org/fest/assertions/StringAssert.java
public @NotNull StringAssert excludes(String s) {
    isNotNull();
    if (actual.indexOf(s) == -1) {
      return this;
    }
    failIfCustomMessageIsSet();
    throw failure(format("<%s> should not contain the String:<%s>", actual, s));
  }
public @NotNull StringAssert excludes(String s) {
    isNotNull();
    if (actual.indexOf(s) == -1) {
      return this;
    }
    failIfCustomMessageIsSet();
    throw failure(format("<%s> should not contain the String:<%s>", actual, s));
  }
Verifies that the actual {@code String} does not contains the given one.

@param s the given {@code String} expected not to be contained in the actual one.
@return this assertion object.
@throws AssertionError if the actual {@code String} is {@code null}.
@throws AssertionError if the actual {@code String} does contain the given one.