Part of the failures are because of symlinks. I get this warning:

Symbolic links enabled on this platform but disabled for this user; run as administrator or use Local Security Policy > Security Settings > Local Policies > User Rights Assignment > Create symbolic links

I ran powershell as an admin (didn't try the part about Local Security Policy yet) and the errors are down to 1

Failed tests:
  RunTest.getLogReturnsAnRightOrder:192 expected:<[...truncated [6]8 B...]> but was:<[...truncated [7]8 B...]>

The issue with this one is that the person who wrote the test didn't take into account Windows line endings which add an additional 10 bytes to the trucated count. A small patch like follows allows that test to pass:

    int byteCount = 68;
    if(Utils.isWindows()) {
        byteCount += 10;
    }
    assertEquals("[...truncated "+byteCount+" B...]", logLines.get(0));

I do get the following error though for the war

[INFO] --- frontend-maven-plugin:1.0:install-node-and-npm (install node and npm) @ jenkins-war ---
[INFO] Installing node version v4.0.0
[INFO] Downloading file:/C:/code/_external/jenkins/war/target/frontend/v4.0.0/win-x86/node.exe to C:\Users\USER\.m2\repository\com\github\eirslett\node\4.0.0\node-4.0.0-windows-x86.exe
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO]
[INFO] Jenkins main module ................................ SUCCESS [  5.636 s]
[INFO] Jenkins cli ........................................ SUCCESS [ 19.834 s]
[INFO] Jenkins core ....................................... SUCCESS [10:58 min]
[INFO] Jenkins war ........................................ FAILURE [ 27.832 s]
[INFO] Tests for Jenkins core ............................. SKIPPED
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 11:53 min
[INFO] Finished at: 2016-12-07T15:37:17-07:00
[INFO] Final Memory: 55M/194M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal com.github.eirslett:frontend-maven-plugin:1.0:install-node-and-npm (install node and npm) on project jenkins-war: Could not download Node.js from: ile:/C:/code/_external/jenkins/war/target/frontend/v4.0.0/win-x86/node.exe: Could not download file:/C:/code/_external/jenkins/war/target/frontend/v4.0.0/win-x86/node.exe: Source 'C:\code\_external\jenkins\war\target\frontend\v4.0.0\win-x86\node.exe' does not exist -> [Help 1]

Is this 32 bit Windows or JDK?

Mine is 64bit for both

My bad, the JDK is 32-bit.

If I switch to a 64-bit JDK, the build completes successfully

christ66 had a patch in progress to remove use of symlinks for build metadata, which would possibly obviate those failures.

I'm looking into a PR for the Jenkinsfile to build on a Windows node as well. This has been missing for a while.

slide_o_mix - note that https://ci.jenkins.io/job/Core_Folder/job/jenkins_master and https://jenkins.ci.cloudbees.com/job/core/job/jenkins-core/ are currently FreeStyle jobs, maybe rtyler knows the reason for this on ci.jenkins.io. jenkins.ci has no windows nodes configured.

The Jenkinsfile in remoting builds on both platforms (but isn't hooked up to anything)

In talking to rtyler on IRC yesterday, there are windows nodes available and the Jenkinsfile is in use at least on some build system.

Mmmmm Jenkinsfile

https://ci.jenkins.io/job/Core/job/jenkins/

https://github.com/jenkins-infra/documentation/blob/03ef2277047fd93d8dc882f8c7a0b32dc76fb99e/ci.adoc#node-labels

I ran powershell as an admin (didn't try the part about Local Security Policy yet) and the errors are down to 1

The tests should have an assumption about symlinks if they require them to pass.
Not looked at the test but I thought there was a fallback that should work for this situation (unless the test is explicitly testing the symlink bit).

OT: I'm paranoid and the MS doc has a big fat warning "Symbolic links can expose security vulnerabilities in applications that aren't designed to handle them" And whilst I am a trusted user, I do not trust all of my applications to do the right thing

Anyway - thanks for looking into this slide_o_mix

Filed https://github.com/jenkinsci/jenkins/pull/2689 against the Jenkinsfile to also build the core on Windows.

teilo Working on ^ I saw there's actually a few failures in the test module of the core. Can you run it too and confirm? (I'm saying "a few" because 60+ is quite high, but still small compared to 9173 ).
Thanks

19:03:20 [windows] Tests run: 9173, Failures: 53, Errors: 11, Skipped: 34, Flakes: 3
19:03:20 [windows] 
19:03:20 [windows] [ERROR] There are test failures.

Created JENKINS-40746 to followup on the failures on that module and not mix discussions (though there's still probably a link).

Code changed in jenkins
User: Daniel Beck
Path:
core/src/test/java/hudson/model/RunTest.java
http://jenkins-ci.org/commit/jenkins/5483ee13833bb44ff611e8da3a8c74379ba26e11
Log:
Merge pull request #2690 from batmat/fix-windows-build

JENKINS-40290 Fix test failing on Windows because of line feed assumption

Compare: https://github.com/jenkinsci/jenkins/compare/6f9837683905...5483ee13833b

@batmat not when I ran it (but make sure you use -Dconcurrency=1 otherwise you have a whole slew of random garbage JENKINS-37177)

I will run again.

Hasn't this been resolved now?

slide_o_mix a lot of the tests where "fixed" by ignoring them on windows. https://ci.jenkins.io/job/Core/job/jenkins/job/master/510/testReport/hudson.model/JobTest/testDoNotAutoTrimExistingUntrimmedNames/

So in one way yes the tests no longer fail - but in another way no - no as there are currently 103 skipped tests and I would guess a large proportion of them are assumeFalse("not on windows" , Functions.isWindows())