[context] Split "env" values and prefixes.

recipe_engine/unittests/step_runner_test.py

Index: recipe_engine/unittests/step_runner_test.py
diff --git a/recipe_engine/unittests/step_runner_test.py b/recipe_engine/unittests/step_runner_test.py
index 152b39efa80e34c460698fb83afdfeefa4bf3484..299563162ad213df42742c1882a2705544410be2 100755
--- a/recipe_engine/unittests/step_runner_test.py
+++ b/recipe_engine/unittests/step_runner_test.py
@@ -3,6 +3,7 @@
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
+import os
 import unittest
 
 import test_env
@@ -53,5 +54,77 @@ class TestLinebuf(unittest.TestCase):
     self.assertEqual("", lb.extra.getvalue())
 
 
+class TestMergeEnvs(unittest.TestCase):
+  def setUp(self):
+    self.original = {
+        'FOO': 'foo',
+    }
+
+  @staticmethod
+  def pathjoin(*parts):
+    return os.pathsep.join(parts)
+
+  def _merge(self, overrides, prefixes):
+    return step_runner._merge_envs(self.original, overrides, prefixes,
+                                   os.pathsep)
+
+  def test_nothing_to_do(self):
+    self.assertEqual(
+        self._merge({}, {}),
+        self.original)
+
+  def test_merge_with_empty_path_tuple(self):
+    self.assertEqual(self._merge(
+      {'FOO': ''}, {'FOO': ()}),
+      {'FOO': ''})
+
+  def test_merge_with_path_tuple(self):
+    self.assertEqual(self._merge(
+      {}, {'BAR': ('bar', 'baz')}),
+      {'FOO': 'foo', 'BAR': self.pathjoin('bar', 'baz')})
+
+  def test_merge_with_path_tuple_and_orig_env(self):
+    self.assertEqual(self._merge(
+      {}, {'FOO': ('bar', 'baz')}),
+      {'FOO': self.pathjoin('bar', 'baz', 'foo')})
+
+  def test_merge_with_path_tuple_and_env(self):
+    self.assertEqual(self._merge(
+      {'FOO': 'override'}, {'FOO': ('bar', 'baz')}),
+      {'FOO': self.pathjoin('bar', 'baz', 'override')})
+
+  def test_merge_with_path_tuple_and_env_subst(self):
+    self.assertEqual(self._merge(
+      {'FOO': 'a-%(FOO)s-b'}, {'FOO': ('bar', 'baz')}),
+      {'FOO': self.pathjoin('bar', 'baz', 'a-foo-b')})
+
+  def test_merge_with_path_tuple_and_env_empty_subst(self):
+    self.original['FOO'] = ''
+    self.assertEqual(self._merge(
+      {'FOO': '%(FOO)s'}, {'FOO': ('bar', 'baz')}),
+      {'FOO': self.pathjoin('bar', 'baz')})
+
+  def test_merge_with_path_tuple_and_env_clear(self):
+    self.assertEqual(self._merge(
+      {'FOO': None}, {'FOO': ('bar', 'baz')}),
+      {'FOO': self.pathjoin('bar', 'baz')})
+
+  def test_merge_with_subst(self):
+    self.assertEqual(self._merge(
+        {'FOO': 'a-%(FOO)s-b'}, {}),
+        {'FOO': 'a-foo-b'})
+
+  def test_merge_with_empty_subst(self):
+    self.original['FOO'] = ''
+    self.assertEqual(self._merge(
+        {'FOO': '%(FOO)s'}, {}),
+        {'FOO': ''})
+
+  def test_merge_with_clear(self):
+    self.assertEqual(self._merge(
+        {'FOO': None}, {}),
+        {})
+
+
 if __name__ == '__main__':
   unittest.main()