title: What is the proper error message to supply to Google Guava's Preconditions.* methods?
body: <p>For example when using <a href="http://guava-libraries.googlecode.com/svn/trunk/javadoc/com/google/common/base/Preconditions.html#checkArgument(boolean,%20java.lang.Object)" rel="noreferrer">Preconditions.checkArgument</a>, is the error message supposed to reflect the passing case or the failing case of the check in question?</p>
  
  <pre><code>import static com.google.common.base.Preconditions.*;
  
  void doStuff(int a, int b) {
    checkArgument(a == b, "a == b");
    // OR
    checkArgument(a == b, "a != b");
  }
  </code></pre>