Python: Update bro_test to reference script directly (#582)

diff --git a/python/tests/_test_utils.py b/python/tests/_test_utils.py
index e38edd3..104e654 100644
--- a/python/tests/_test_utils.py
+++ b/python/tests/_test_utils.py
@@ -13,9 +13,9 @@
 src_dir = os.path.join(project_dir, 'python')
 test_dir = os.path.join(project_dir, 'tests')
 
-PYTHON = sys.executable or 'python'
-
-BRO = os.path.join(src_dir, 'bro.py')
+python_exe = sys.executable or 'python'
+bro_path = os.path.join(src_dir, 'bro.py')
+BRO_ARGS = [python_exe, bro_path]
 
 # Get the platform/version-specific build folder.
 # By default, the distutils build base is in the same location as setup.py.
diff --git a/python/tests/bro_test.py b/python/tests/bro_test.py
index c0d55dc..b55129d 100644
--- a/python/tests/bro_test.py
+++ b/python/tests/bro_test.py
@@ -9,8 +9,7 @@
 from . import _test_utils
 import brotli
 
-PYTHON = _test_utils.PYTHON
-BRO = _test_utils.BRO
+BRO_ARGS = _test_utils.BRO_ARGS
 TEST_ENV = _test_utils.TEST_ENV
 
 
@@ -28,13 +27,12 @@
 
     def _decompress_file(self, test_data):
         temp_uncompressed = _test_utils.get_temp_uncompressed_name(test_data)
-        args = [PYTHON, BRO, '-f', '-d', '-i', test_data, '-o',
-                temp_uncompressed]
+        args = BRO_ARGS + ['-f', '-d', '-i', test_data, '-o', temp_uncompressed]
         subprocess.check_call(args, env=TEST_ENV)
 
     def _decompress_pipe(self, test_data):
         temp_uncompressed = _test_utils.get_temp_uncompressed_name(test_data)
-        args = [PYTHON, BRO, '-d']
+        args = BRO_ARGS + ['-d']
         with open(temp_uncompressed, 'wb') as out_file:
             with open(test_data, 'rb') as in_file:
                 subprocess.check_call(
@@ -61,14 +59,14 @@
         temp_uncompressed = _test_utils.get_temp_uncompressed_name(test_data)
         temp_compressed = _test_utils.get_temp_compressed_name(test_data)
         original = test_data
-        args = [PYTHON, BRO, '-f', '-d']
+        args = BRO_ARGS + ['-f', '-d']
         args.extend(['-i', temp_compressed, '-o', temp_uncompressed])
         subprocess.check_call(args, env=TEST_ENV)
         self.assertFilesMatch(temp_uncompressed, original)
 
     def _compress_file(self, test_data, **kwargs):
         temp_compressed = _test_utils.get_temp_compressed_name(test_data)
-        args = [PYTHON, BRO, '-f']
+        args = BRO_ARGS + ['-f']
         if 'quality' in kwargs:
             args.extend(['-q', str(kwargs['quality'])])
         if 'lgwin' in kwargs:
@@ -78,7 +76,7 @@
 
     def _compress_pipe(self, test_data, **kwargs):
         temp_compressed = _test_utils.get_temp_compressed_name(test_data)
-        args = [PYTHON, BRO]
+        args = BRO_ARGS
         if 'quality' in kwargs:
             args.extend(['-q', str(kwargs['quality'])])
         if 'lgwin' in kwargs:
diff --git a/python/tests/decompressor_test.py b/python/tests/decompressor_test.py
old mode 100755
new mode 100644