KAFKA-3237 - Remove test cases testInvalidDefaultRange() and testInva…

[jcustenborder]

Remove test cases testInvalidDefaultRange() and testInvalidDefaultString(). Defaults if not overridden will get checked on parse. Testing the defaults is unnecessary. This allows you to set that a parameter is required while setting a validator for that parameter. Added a test case testNullDefaultWithValidator that allows a null default with a validator for certain strings.

[granthenke]

If the goal is to have a required parameter with a validator, an alternative solution would be to add a new method to ConfigDef that accepts a validator with no default. The problem is it collides with the existing signature that accepts a default Object with no validator.

public ConfigDef define(String name, Type type, Object defaultValue, Importance importance, String documentation)
...
public ConfigDef define(String name, Type type, Validator validator, Importance importance, String documentation)

Perhaps a fix utilizing ConfigDef.NO_DEFAULT_VALUE could work. It would need to be made public. Then the validator check that was removed could be changed to:

if (this.validator != null && this.hasDefault())
  this.validator.ensureValid(name, defaultValue);

The reason I am not a fan of the existing change is that null really isn't a valid default, and if a default is defined, it is assumed that the parameter is not required and whatever is set should be valid in the provided validator. The provided default of null will also be printed in the generated docs output and sorted as if it not required. Example: http://kafka.apache.org/documentation.html#producerconfigs

[jcustenborder]

@granthenke I didn't think about the documentation generation use case. I'll add the correct this and resubmit.

[ewencp]

LGTM