test: accept Python 3 in test-find-python.js

Fixes: https://github.com/nodejs/node-gyp/issues/1826
PR-URL: https://github.com/nodejs/node-gyp/pull/1843
Reviewed-By: Christian Clauss <cclauss@me.com>
Reviewed-By: Rod Vagg <r@va.gg>
Reviewed-By: Matt Cowley <me@mattcowley.co.uk>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>

.travis.yml

@@ -62,7 +62,8 @@ matrix:
       before_install: choco install python
 
   allow_failures:
-    - env: NODE_GYP_FORCE_PYTHON=python3 EXPERIMENTAL_NODE_GYP_PYTHON3=1
+    - os: osx
+      env: NODE_GYP_FORCE_PYTHON=python3 EXPERIMENTAL_NODE_GYP_PYTHON3=1
     - env: >-
         PATH=/c/Python37:/c/Python37/Scripts:$PATH
         NODE_GYP_FORCE_PYTHON=/c/Python37/python.exe

test/test-find-python.js

@@ -1,13 +1,12 @@
 'use strict'
 
+delete process.env.PYTHON
+
 const test = require('tap').test
 const findPython = require('../lib/find-python')
 const execFile = require('child_process').execFile
 const PythonFinder = findPython.test.PythonFinder
 
-delete process.env.PYTHON
-delete process.env.NODE_GYP_FORCE_PYTHON
-
 require('npmlog').level = 'warn'
 
 test('find python', function (t) {
@@ -17,8 +16,13 @@ test('find python', function (t) {
     t.strictEqual(err, null)
     var proc = execFile(found, ['-V'], function (err, stdout, stderr) {
       t.strictEqual(err, null)
+      if (/Python 2/.test(stderr)) {
         t.strictEqual(stdout, '')
         t.ok(/Python 2/.test(stderr))
+      } else {
+        t.ok(/Python 3/.test(stdout))
+        t.strictEqual(stderr, '')
+      }
     })
     proc.stdout.setEncoding('utf-8')
     proc.stderr.setEncoding('utf-8')
@@ -51,6 +55,7 @@ TestPythonFinder.prototype.log = {
   warn: () => {},
   error: () => {}
 }
+delete TestPythonFinder.prototype.env.NODE_GYP_FORCE_PYTHON
 
 test('find python - python', function (t) {
   t.plan(6)