@Test
  public void regexpPattern() throws IOException {
    BsonRegularExpression value = new BsonRegularExpression("abc");
    check(Jsons.readerAt(value).peek()).is(JsonToken.STRING);
    check(Jsons.readerAt(value).nextString()).is("abc");
    check(Jsons.readerAt(new BsonRegularExpression(".*")).nextString()).is(".*");
  }
Validate type conversion between BSON and gson-JSON ({@link com.google.gson.stream.JsonToken}).
mongo/test/org/immutables/mongo/bson4gson/TypeConversionTest.java