jdk contract tests

'com.github.nwillc:contracts:1.6.4'

<dependency>
	<groupId>com.github.nwillc</groupId>
	<artifactId>contracts</artifactId>
	<version>1.6.4</version>
</dependency>

<dependency org="com.github.nwillc" name="contracts" rev="1.6.4"/>

"com.github.nwillc", "contracts", "1.6.4"