lib/subject/objectSubject.js
function FieldValue(subject, name, value) {
  this.subject = subject;
  this.name = name;
  this.value = subject.value[name];
  this.format = subject.format;
}
function FieldValue(subject, name, value) {
  this.subject = subject;
  this.name = name;
  this.value = subject.value[name];
  this.format = subject.format;
}
A fluent context object containing the value of the field that was just tested. Used for
additional assertions about a field.
@constructor