There are few places where the sun.misc.IOUtils.realFully(InputStream, int, boolean) is used directly and one place where it is just copied.

These tests directly use sun.misc.IOUtils:
java/lang/annotation/AnnotationType/AnnotationTypeRuntimeAssumptionTest.java
java/lang/reflect/Method/InterfaceStatic/StaticInterfaceMethodInWayOfDefault.java
sun/security/tools/jarsigner/EntriesOrder.java

In this test, realFully(InputStream) repeats the one from sun.misc.IOUtils with the exception of omitted parameters:
java/lang/invoke/lambda/LambdaClassLoaderSerialization.java

This one test is itself a test for IOUtils.readFully, so should not be changed:
sun/security/util/DerValue/BadValue.java

There are more readFully methods in the tests, they have different implementations, so should be left intact:
java/util/zip/InflateIn_DeflateOut.java
java/util/zip/GZIP/Accordion.java
sun/net/www/protocol/http/RedirectOnPost.java
sun/net/www/protocol/jar/jarbug/src/test/JarTest.java