Tests to examine:

open/test/jdk/java/net/ipv6tests/Tests.java --- base Test class not run directly
open/test/jdk/java/net/HugeDataTransferTest.java -- isWindows to obtain windows specific settings
open/test/jdk/java/net/NetworkInterface/IndexTest.java -- Windows OS check to avoid Teredo interface (could be refactored to use NetworkConfiguration)
open/test/jdk/java/net/NetworkInterface/Test.java -- Windows OS check to avoid Teredo interface
open/test/jdk/java/net/NetworkInterface/Equals.java -- Windows OS check to avoid Teredo interface
open/test/jdk/java/net/NetworkInterface/NetworkInterfaceStreamTest.java -- Windows OS check to avoid Teredo interface
open/test/jdk/java/net/Inet6Address/serialize/Inet6AddressSerializationTest.java -- Windows OS check to avoid Teredo interface
open/test/jdk/java/net/httpclient/websocket/PendingOperations.java -- Windows and macOS OS check to enable test repeat policy
open/test/jdk/java/net/Inet4Address/PingThis.java -- uses @require not run on Windows
open/test/jdk/java/net/URLConnection/6212146/TestDriver.java -- Windows OS check to enable windows specific config of process cmd

open/test/jdk/java/net/DatagramSocket/InheritHandle.java -- Windows OS check to enable Windows retry policy
open/test/jdk/java/net/DatagramSocket/Send12k.java -- macOS check to enable macOS specific setting
open/test/jdk/java/net/MulticastSocket/TestInterfaces.java -- Windows OS check to avoid Teredo interface
open/test/jdk/java/net/MulticastSocket/SetOutgoingIf.java -- macOS check to avoid using macOS tunnelling interface
open/test/jdk/java/net/MulticastSocket/Promiscuous.java -- Linux OS check to NOT use older versions c.f. PromiscuousIPv6.java for @requires usage. *****
open/test/jdk/java/net/MulticastSocket/PromiscuousIPv6.java -- uses @requires
open/test/jdk/java/net/MulticastSocket/NoLoopbackPackets.java -- uses @requires os.family != "windows"
open/test/jdk/java/net/ServerSocket/AnotherSelectFdsLimit.java -- uses @requires os.family == "mac"
open/test/jdk/java/net/ServerSocket/SelectFdsLimit.java -- uses @requires os.family == "mac"
open/test/jdk/sun/net/www/protocol/file/FileURLTest.java -- can be converted to use @requires os.family == "windows" ***
open/test/jdk/sun/net/www/http/HttpURLConnection/BasicNTLMAuthTest.java -- Windows OS check to set windows specific Authenticator
open/test/jdk/com/sun/net/httpserver/simpleserver/jwebserver/CommandLinePortNotSpecifiedTest.java -- Windows OS check to set up windows specific os command exe syntax
open/test/jdk/com/sun/net/httpserver/simpleserver/jwebserver/MaxRequestTimeTest.java -- Windows OS check to set up windows specific os command exe syntax
open/test/jdk/com/sun/net/httpserver/simpleserver/jwebserver/CommandLineNegativeTest.java -- Windows OS check to set up windows specific os command exe syntax
open/test/jdk/com/sun/net/httpserver/simpleserver/jwebserver/CommandLinePositiveTest.java -- Windows OS check to set up windows specific os command exe syntax
open/test/jdk/com/sun/net/httpserver/simpleserver/CommandLinePortNotSpecifiedTest.java -- Windows OS check to set up windows specific os command exe syntax
open/test/jdk/com/sun/net/httpserver/simpleserver/CommandLineNegativeTest.java -- Windows OS check to set up windows specific os command exe syntax
open/test/jdk/com/sun/net/httpserver/simpleserver/CommandLinePositiveTest.java -- Windows OS check to set up windows specific os command exe syntax


Most of these tests probably only have conditional logic.