Migrate tests/bin/test_jsonpath.py to use pytest

Also, the empty `__init__.py` in the same directory has been deleted;
pytest doesn't rely on test suites being importable modules.

Also, these tools were run against the test file:

* pyupgrade --py37-plus
* black
* isort

tests/bin/test_jsonpath.py

@@ -1,53 +1,37 @@
-# Standard library imports
-import unittest
-import logging
+"""
+Tests for the jsonpath.py command line interface.
+"""
+
 import io
-import sys
-import os
 import json
+import os
+import sys
 
 from jsonpath_ng.bin.jsonpath import main
 
-class TestJsonPathScript(unittest.TestCase):
-    """
-    Tests for the jsonpath.py command line interface.
-    """
-
-    @classmethod
-    def setup_class(cls):
-        logging.basicConfig()
-
-    def setUp(self):
-        self.input = io.StringIO()
-        self.output = io.StringIO()
-        self.saved_stdout = sys.stdout
-        self.saved_stdin = sys.stdin
-        sys.stdout = self.output
-        sys.stdin = self.input
-
-    def tearDown(self):
-        self.output.close()
-        self.input.close()
-        sys.stdout = self.saved_stdout
-        sys.stdin = self.saved_stdin
-
-    def test_stdin_mode(self):
-        # 'format' is a benign Python 2/3 way of ensuring it is a text type rather than binary
-        self.input.write('{0}'.format(json.dumps({
-            'foo': {
-                'baz': 1,
-                'bizzle': {
-                    'baz': 2
-                }
-            }
-        })))
-        self.input.seek(0)
-        main('jsonpath.py', 'foo..baz')
-        self.assertEqual(self.output.getvalue(), '1\n2\n')
-
-    def test_filename_mode(self):
-        test1 = os.path.join(os.path.dirname(__file__), 'test1.json')
-        test2 = os.path.join(os.path.dirname(__file__), 'test2.json')
-        main('jsonpath.py', 'foo..baz', test1, test2)
-        self.assertEqual(self.output.getvalue(), '1\n2\n3\n4\n')
 
+def test_stdin_mode(monkeypatch, capsys):
+    stdin_text = json.dumps(
+        {
+            "foo": {
+                "baz": 1,
+                "bizzle": {"baz": 2},
+            },
+        }
+    )
+    monkeypatch.setattr(sys, "stdin", io.StringIO(stdin_text))
+
+    main("jsonpath.py", "foo..baz")
+
+    stdout, _ = capsys.readouterr()
+    assert stdout == "1\n2\n"
+
+
+def test_filename_mode(capsys):
+    test1 = os.path.join(os.path.dirname(__file__), "test1.json")
+    test2 = os.path.join(os.path.dirname(__file__), "test2.json")
+
+    main("jsonpath.py", "foo..baz", test1, test2)
+
+    stdout, _ = capsys.readouterr()
+    assert stdout == "1\n2\n3\n4\n"