[foreign] RFR 8216284: Make sure test jars are deleted before/after tests

[Jorn Vernee]

Hi,

I was seeing some errors while running the JextractToolProviderTest 
test, but the test still passed. The errors were from the test jars not 
being able to be deleted because some process was using the file. It 
turns out this was due to JextractToolRunner::loadClass creating a 
URLClassLoader to load classes from the jar, but the classloader never 
being closed causing the file to still be in use when trying to delete 
it. This was throwing IOExceptions which were being printed, but 
otherwise ignored.

With all the errors being thrown and ignored I wasn't sure whether I 
could trust the outcome of the test. Different tests could also possibly 
interfere with each other if they use the same jar file name and the jar 
doesn't get deleted after each test.

I've solved the problem by replacing the loadClass method with a 
classLoader method which returns an AutoCloseable Loader through which 
the classes can be loaded. The close() method on Loader closes the class 
loader. I have also turned the errors I was seeing into hard errors to 
make sure that the tests fail if an IOException occurs unexpectedly. To 
make that possible I switched JextractToolRunner::deleteFile to using 
Files.deleteIfExtists instead of delete so that an error will not occur 
when it is called at the start of a test but there's nothing to delete.

JextractToolRunner::classLoader is called with a list of Paths to use as 
class path entries e.g.:

     Path helloJar = getOutputFilePath("hello.jar");
     deleteFile(helloJar); // make sure jar does not exist at start of 
test
     Path helloH = getInputFilePath("hello.h");
     run("-o", helloJar.toString(), helloH.toString()).checkSuccess(); // 
create the jar
     try(Loader loader = classLoader(helloJar)) {
         // ... do tests
     } finally { // class loader is closed after try-block
         deleteFile(helloJar); // now succeeds to delete jar
     }

I've replaced calls to loadClass with calls to Loader::loadClass, also 
adding a call to JextractToolRunner::classLoader to the enclosing 
try-blocks. I've also made sure jars are being deleted before /after a 
test in some places where that was not being done.

Bug: https://bugs.openjdk.java.net/browse/JDK-8216284
Webrev: 
http://cr.openjdk.java.net/~jvernee/panama/webrevs/8216284/webrev.03/

Thanks,
Jorn