Remove unit test runtime dependencies on resources (pantsbuild#8066)

### Problem
Currently, `test_base.py`, `jvm_tool_task_test_base.py`, and `interpreter_cache_test_mixin.py` have implicit runtime dependencies on files defined at the build root, specifically `./pants`, `./BUILD.tools`, `3rdparty/BUILD`, and `.pants.d`. 

Because V2 is completely hermetic, these runtime dependencies fail to resolve as the test runner does not know to copy the files into the snapshot. Instead, we need some way to explicitly mark these dependencies via the `BUILD` file or to remove the dependency outright.

#### FYI: why didn't we detect this earlier?
We've been using V2 to run unit tests in CI for the past two months. Why didn't we detect this? The reason is that V2 runs locally in `.pantsd`, and the logic to get the buildroot traverses ancestors.

This was only detected when running unit tests with remote execution.

### Solution
* Remove the dependency on `./pants`, which was not actually needed. 
* Explicitly depend on `./BUILD.tools` and `3rdparty/BUILD`. 
* Remove `interpreter_cache_test_mixin.py`, which is inherently non-hermetic and cannot work with the V2 model. Even though this has a slight performance impact, this is offset by the remote caching we will now be able to get + having more sound / hermitic tests.

BUILD

@@ -0,0 +1,12 @@
+# Copyright 2019 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+files(
+  name = 'build_tools',
+  source = 'BUILD.tools',
+)
+
+files(
+  name = '3rdparty_build',
+  source = '3rdparty/BUILD',
+)

tests/python/pants_test/backend/project_info/tasks/BUILD

@@ -63,7 +63,6 @@ python_tests(
     'src/python/pants/util:osutil',
     'tests/python/pants_test/subsystem:subsystem_utils',
     'tests/python/pants_test:task_test_base',
-    'tests/python/pants_test/backend/python/tasks:interpreter_cache_test_mixin',
   ]
 )
 

tests/python/pants_test/backend/project_info/tasks/test_export.py

@@ -31,12 +31,11 @@
 from pants.util.contextutil import temporary_dir
 from pants.util.dirutil import chmod_plus_x, safe_open
 from pants.util.osutil import get_os_name, normalize_os_name
-from pants_test.backend.python.tasks.interpreter_cache_test_mixin import InterpreterCacheTestMixin
 from pants_test.subsystem.subsystem_util import init_subsystems
 from pants_test.task_test_base import ConsoleTaskTestBase
 
 
-class ExportTest(InterpreterCacheTestMixin, ConsoleTaskTestBase):
+class ExportTest(ConsoleTaskTestBase):
   @classmethod
   def task_type(cls):
     return Export

tests/python/pants_test/backend/python/tasks/BUILD

@@ -1,16 +1,10 @@
 # Copyright 2016 Pants project contributors (see CONTRIBUTORS.md).
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
-python_library(
-  name='interpreter_cache_test_mixin',
-  sources=['interpreter_cache_test_mixin.py'],
-)
-
 python_library(
   name='python_task_test_base',
   sources=['python_task_test_base.py'],
   dependencies=[
-    ':interpreter_cache_test_mixin',
     'src/python/pants/backend/python:plugin',
     'src/python/pants/backend/python/targets',
     'src/python/pants/build_graph',

tests/python/pants_test/backend/python/tasks/python_task_test_base.py

@@ -9,7 +9,6 @@
 from pants.backend.python.register import build_file_aliases as register_python
 from pants.backend.python.targets.python_binary import PythonBinary
 from pants.build_graph.address import Address
-from pants_test.backend.python.tasks.interpreter_cache_test_mixin import InterpreterCacheTestMixin
 from pants_test.subsystem import subsystem_util
 from pants_test.task_test_base import TaskTestBase
 
@@ -35,7 +34,7 @@ def normalized_current_platform():
   return normalize_platform_tag(pep425tags.get_platform())
 
 
-class PythonTaskTestBase(InterpreterCacheTestMixin, TaskTestBase):
+class PythonTaskTestBase(TaskTestBase):
   """
   :API: public
   """

tests/python/pants_test/jvm/BUILD

@@ -23,6 +23,8 @@ python_library(
   name='jvm_tool_task_test_base',
   sources=['jvm_tool_task_test_base.py'],
   dependencies=[
+    '//:build_tools',
+    '//:3rdparty_build',
     ':jvm_task_test_base',
     'src/python/pants/backend/jvm/subsystems:jvm_tool_mixin',
     'src/python/pants/backend/jvm/targets:jvm',
@@ -33,6 +35,7 @@ python_library(
     'src/python/pants/build_graph',
     'src/python/pants/ivy',
     'src/python/pants/java/jar',
+    'src/python/pants/util:dirutil',
   ]
 )
 

tests/python/pants_test/jvm/jvm_tool_task_test_base.py

@@ -65,12 +65,11 @@ def setUp(self):
                                read_from=artifact_caches,
                                write_to=artifact_caches)
 
-    # Tool option defaults currently point to targets in the real BUILD.tools, so we copy it and
-    # its dependency BUILD files into our test workspace.
-    shutil.copy(os.path.join(self.real_build_root, 'BUILD.tools'), self.build_root)
-    third_party = os.path.join(self.build_root, '3rdparty')
-    safe_mkdir(third_party)
-    shutil.copy(os.path.join(self.real_build_root, '3rdparty', 'BUILD'), third_party)
+    # Copy into synthetic build-root
+    shutil.copy('BUILD.tools', self.build_root)
+    build_root_third_party = os.path.join(self.build_root, '3rdparty')
+    safe_mkdir(build_root_third_party)
+    shutil.copy(os.path.join('3rdparty', 'BUILD'), build_root_third_party)
 
     Bootstrapper.reset_instance()
 

tests/python/pants_test/test_base.py

@@ -366,7 +366,6 @@ def pants_workdir(self):
   @classmethod
   @memoized_method
   def _build_root(cls):
-    cls.real_build_root = BuildRoot().path
     return os.path.realpath(mkdtemp(suffix='_BUILD_ROOT'))
 
   @classmethod