[context] Split "env" values and prefixes.

recipe_modules/context/tests/env.py

 # 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.
 
 DEPS = [
-  "context",
-  "path",
-  "step",
+  'context',
+  'path',
+  'raw_io',
+  'step',
 ]
 
 
+# This key is set by "//recipe_engine/unittests/run_test.py" to "default". This
+# causes predictable results when run via "run_test", allowing us to test
+# correct expression of environment variables in production.
+_KEY = 'RECIPE_ENGINE_CONTEXT_TEST'
+
+
 def RunSteps(api):
   api.step('no env', ['echo', 'hello'])
 
-  with api.context(env={"SOMETHING": "1"}):
+  with api.context(env={'SOMETHING': '1'}):
     api.step('with env', ['echo', 'hello'])
 
-    with api.context(env={"SOMETHING_ELSE": "0"}):
+    with api.context(env={'SOMETHING_ELSE': '0'}):
       api.step('with 2 envs', ['echo', 'hello'])
 
-  with api.context(env={'FOO': 'bar'}):
-    api.step('env step', ['bash', '-c', 'echo $FOO'])
+  # The following tests use "expect_step". In simulation mode, this will always
+  # pass. However, when run through "run" or via "unittests/run_test.py", this
+  # will process the real output environment variables and assert that they
+  # match expectations.
+  def expect_step(name, exp):
+    result = api.step(
+        name,
+        ['bash', '-c', 'echo -n $'+_KEY],
+        stdout=api.raw_io.output(),
+        step_test_data=lambda: api.raw_io.test_api.stream_output(exp),
+    )
+    assert result.stdout == exp, (
+        '%r did not equal expected %r' % (result.stdout, exp))
 
-    base_path = 'foo%s%%(FOO)s%sbaz' % (api.path.pathsep, api.path.pathsep)
-    with api.context(env={'FOO': base_path}):
-      api.step('env step augmented', ['bash', '-c', 'echo $FOO'])
+  expect_step('default', 'default')
 
-      pants = api.path['start_dir'].join('pants')
-      shirt = api.path['start_dir'].join('shirt')
-      with api.context(env={'FOO': api.context.Prefix(pants, shirt)}):
-        api.step('env step with prefix', ['bash', '-c', 'echo $FOO'])
+  # Can cause envvars to be dropped completely.
+  with api.context(env={_KEY: None}):
+    expect_step('drop', '')
+
+  pants = api.path['start_dir'].join('pants')
+  shirt = api.path['start_dir'].join('shirt')
+  with api.context(env={_KEY: 'bar'}):
+    expect_step('env step', 'bar')
+
+    base_path = api.path.pathsep.join(['foo', '%('+_KEY+')s', 'bar'])
+    with api.context(env={_KEY: base_path}):
+      expect_step('env step augmented',
+          api.path.pathsep.join(['foo', 'default', 'bar']))
+
+      with api.context(env_prefixes={_KEY: [pants, shirt]}):
+        expect_step('env step with prefix',
+            api.path.pathsep.join([str(pants), str(shirt), 'foo',
+                                   'default', 'bar']))
 
   # Can set the path of default environment variables.
-  with api.context(env={'FOO': api.context.Prefix(shirt)}):
-    api.step('env with default value',
-             ['bash', '-c', 'echo $FOO'])
+  with api.context(env_prefixes={_KEY: [shirt]}):
+    expect_step('env with default value',
+        api.path.pathsep.join([str(shirt), 'default']))
 
-  # Can cause envvars to be dropped completely.
-  with api.context(env={"PYTHONPATH": None}):
-    api.step('drop PYTHONPATH', ['bash', '-c', 'set'])
+    # When 'env' is also defined, appends it.
+    with api.context(env={_KEY: 'foo'}):
+      expect_step('env with override value',
+            api.path.pathsep.join([str(shirt), 'foo']))
+
+    # When "env" is explicitly cleared, does not append.
+    with api.context(env={_KEY: None}):
+      expect_step('env with cleared value', str(shirt))
+
+    # When "env" is explicitly empty, does not append.
+    with api.context(env={_KEY: ''}):
+      expect_step('env with empty value', str(shirt))
 
 
 def GenTests(api):
   yield api.test('basic')