Mimic patch for decorator and pytest fixtures (#77)

* Mimic patch for decorator and pytest fixtures
Fix #75

* Fix flake8

Co-authored-by: Frédéric Collonval <frederic.collonval@ariadnext.com>

testbook/testbook.py

@@ -1,15 +1,30 @@
-import nbformat
+import functools
+from unittest.mock import DEFAULT
 
-try:
-    from pytest import fixture
-except ImportError:  # pragma: no cover
-    def fixture(func, *args, **kwargs):
-        return func
+import nbformat
 
 from .client import TestbookNotebookClient
 
 
 class testbook:
+    """`testbook` acts as function decorator or a context manager.
+
+    When the function/with statement exits the kernels started when
+    entering the function/with statement will be terminated.
+
+    If `testbook` is used as a decorator, the `TestbookNotebookClient`
+    will be passed as first argument to the decorated function.
+    """
+    # Developer notes:
+    #
+    # To trick pytest, we mimic the API of unittest.mock.patch in testbook.
+    # Notably, the following elements are added:
+    # * attribute_name, Class attribute (see below)
+    # * new, Instance attribute (see __init__)
+    # * patchings, wrapper attributes (see __call__)
+
+    attribute_name = None
+
     def __init__(self, nb, execute=None, timeout=60, kernel_name='python3', allow_errors=False):
         self.execute = execute
         self.client = TestbookNotebookClient(
@@ -19,6 +34,8 @@ def __init__(self, nb, execute=None, timeout=60, kernel_name='python3', allow_er
             kernel_name=kernel_name
         )
 
+        self.new = DEFAULT
+
     def _prepare(self):
         if self.execute is True:
             self.client.execute()
@@ -34,12 +51,11 @@ def __exit__(self, *args):
         self.client._cleanup_kernel()
 
     def __call__(self, func):
+        @functools.wraps(func)
         def wrapper(*args, **kwargs):  # pragma: no cover
             with self.client.setup_kernel():
                 self._prepare()
                 func(self.client, *args, **kwargs)
 
-        wrapper.__name__ = func.__name__
-        wrapper.__doc__ = func.__doc__
-
-        return fixture(wrapper)
+        wrapper.patchings = [self]
+        return wrapper

testbook/tests/test_testbook.py

@@ -32,6 +32,12 @@ def test_testbook_decorator_with_markers(nb, cell_index_args, expected_result):
     assert nb._cell_index(cell_index_args) == expected_result
 
 
+@pytest.mark.parametrize("cell_index_args, expected_result", [(2, 2), ('hello', 1)])
+@testbook('testbook/tests/resources/inject.ipynb', execute=True)
+def test_testbook_decorator_with_markers_order_does_not_matter(nb, cell_index_args, expected_result):
+    assert nb._cell_index(cell_index_args) == expected_result
+
+
 def test_testbook_execute_all_cells_context_manager():
     with testbook('testbook/tests/resources/inject.ipynb', execute=True) as tb:
         for cell in tb.cells[:-1]: