javagit/src/main/java/edu/nyu/cs/javagit/utilities/CheckUtilities.java
public static void checkDirectoryArgument(File fileName, String variableName) {
    checkNullArgument(fileName, variableName);
    if (!fileName.isDirectory()) {
      throw new IllegalArgumentException(ExceptionMessageMap.getMessage("000007")
          + "  { variableName=[" + variableName + "] }");
    }
  }
public static void checkDirectoryArgument(File fileName, String variableName) {
    checkNullArgument(fileName, variableName);
    if (!fileName.isDirectory()) {
      throw new IllegalArgumentException(ExceptionMessageMap.getMessage("000007")
          + "  { variableName=[" + variableName + "] }");
    }
  }
Checks a <code>File</code> argument to make sure that it is a directory. If not
<code>IllegalArgumentException</code> is thrown.

@param fileName
The <code>File</code> to be checked.
@param variableName
The name of the variable being checked; for use in exception messages.