Fix recipes.py test train when on-disk expectation files are invalid

unittests/test_test.py

 #!/usr/bin/env python
 # Copyright 2017 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 import json
 import os
 import shutil
 import subprocess
 import sys
@@ skipping 727 matching lines @@
     self._run_recipes('test', 'train', '--json', self.json_path)
     expect_path = os.path.join(rw.expect_dir, 'basic.json')
     with open(expect_path) as f:
       expect_contents = json.load(f)
     self.assertEqual(
         [{u'cmd': [u'echo', u'bar'], u'name': u'test'},
          {u'status_code': 0, u'recipe_result': None, u'name': u'$result'}],
         expect_contents)
     self.assertEqual(self.json_generator.get(), self.json_contents)
 
+  def test_train_invaid_json(self):
+    # 1. Initial state: recipe expectations are passing.
+    rw = RecipeWriter(os.path.join(self._root_dir, 'recipes'), 'foo')
+    rw.RunStepsLines = ['pass']
+    rw.add_expectation('basic')
+    rw.write()
+    self._run_recipes('test', 'run', '--json', self.json_path)
+    self.assertEqual(self.json_generator.get(), self.json_contents)
+
+    # 2. Change the expectation and verify tests would fail.
+    expect_path = os.path.join(rw.expect_dir, 'basic.json')
+    with open(expect_path, 'w') as f:
+      f.write('\n'.join([
+          'not valid JSON',
+          '<<<<<',
+          'merge conflict',
+          '>>>>>',
+      ]))
+    with self.assertRaises(subprocess.CalledProcessError) as cm:
+      self._run_recipes('test', 'run', '--json', self.json_path)
+    self.assertIn('foo.basic failed', cm.exception.output)
+    self.assertEqual(
+        self.json_generator
+            .internal_failure('foo.basic')
+            .invalid()
+            .unused_expectation('recipes/foo.expected')
+            .unused_expectation('recipes/foo.expected/basic.json')
+            .coverage_failure('recipes/foo.py', [6])
+            .get(),
+        self.json_contents)
+
+    # 3. Make sure training the recipe succeeds and produces correct results.
+    self._run_recipes('test', 'train', '--json', self.json_path)
+    with open(expect_path) as f:
+      expect_contents = json.load(f)
+    self.assertEqual(
+        [{u'status_code': 0, u'recipe_result': None, u'name': u'$result'}],
+        expect_contents)
+    self.assertEqual(self.json_generator.get(), self.json_contents)
+
   def test_train_checks_coverage(self):
     rw = RecipeWriter(os.path.join(self._root_dir, 'recipes'), 'foo')
     rw.RunStepsLines = ['if False:', '  pass']
     rw.add_expectation('basic')
     rw.write()
     with self.assertRaises(subprocess.CalledProcessError) as cm:
       self._run_recipes('test', 'train', '--json', self.json_path)
     self.assertIn('FATAL: Insufficient coverage', cm.exception.output)
     self.assertNotIn('CHECK(FAIL)', cm.exception.output)
     self.assertNotIn('foo.basic failed', cm.exception.output)
@@ skipping 414 matching lines @@
             .check_failure('bar_check', 'bar_file', 2, 'bar_func', ['bar_args'])
             .internal_failure('bar_internal')
             .uncovered_module('bar_module')
             .unused_expectation('bar_expectation')
             .get(),
         self.json_contents)
 
 
 if __name__ == '__main__':
   sys.exit(unittest.main())