Add --deselect command line option

Fixes pytest-dev#3198

AUTHORS

@@ -97,6 +97,7 @@ Jon Sonesen
 Jonas Obrist
 Jordan Guymon
 Jordan Moldow
+Jordan Speicher
 Joshua Bronson
 Jurko Gospodnetić
 Justyna Janczyszyn

_pytest/main.py

@@ -66,6 +66,8 @@ def pytest_addoption(parser):
                     help="try to interpret all arguments as python packages.")
     group.addoption("--ignore", action="append", metavar="path",
                     help="ignore path during collection (multi-allowed).")
+    group.addoption("--deselect", action="append", metavar="item",
+                    help="deselect item during collection (multi-allowed).")
     # when changing this to --conf-cut-dir, config.py Conftest.setinitial
     # needs upgrading as well
     group.addoption('--confcutdir', dest="confcutdir", default=None,
@@ -208,6 +210,24 @@ def pytest_ignore_collect(path, config):
     return False
 
 
+def pytest_collection_modifyitems(items, config):
+    excludeopt = config.getoption("deselect")
+    if excludeopt is None:
+        return
+
+    remaining = []
+    deselected = []
+    for colitem in items:
+        if colitem.nodeid in excludeopt:
+            deselected.append(colitem)
+        else:
+            remaining.append(colitem)
+
+    if deselected:
+        config.hook.pytest_deselected(items=deselected)
+        items[:] = remaining
+
+
 @contextlib.contextmanager
 def _patched_find_module():
     """Patch bug in pkgutil.ImpImporter.find_module

changelog/3198.feature.rst

@@ -0,0 +1 @@
+Add command line option ``--deselect`` to allow deselection of individual tests at collection time.

doc/en/example/pythoncollection.rst

@@ -39,6 +39,14 @@ you will see that ``pytest`` only collects test-modules, which do not match the
 
     ======= 5 passed in 0.02 seconds =======
 
+Deselect tests during test collection
+-------------------------------------
+
+Tests can individually be deselected during collection by passing the ``--deselect=item`` option.
+For example, say ``tests/foobar/test_foobar_01.py`` contains ``test_a`` and ``test_b``.
+You can run all of the tests within ``tests/`` *except* for ``tests/foobar/test_foobar_01.py::test_a``
+by invoking ``pytest`` with ``--deselect tests/foobar/test_foobar_01.py::test_a``.
+``pytest`` allows multiple ``--deselect`` options.
 
 Keeping duplicate paths specified from command line
 ----------------------------------------------------

testing/test_session.py

@@ -240,6 +240,16 @@ def test_exclude(testdir):
     result.stdout.fnmatch_lines(["*1 passed*"])
 
 
+def test_deselect(testdir):
+    testdir.makepyfile(test_a="""
+        def test_a1(): pass
+        def test_a2(): pass
+    """)
+    result = testdir.runpytest("--deselect=test_a.py::test_a2")
+    assert result.ret == 0
+    result.stdout.fnmatch_lines(["*1 passed, 1 deselected*"])
+
+
 def test_sessionfinish_with_start(testdir):
     testdir.makeconftest("""
         import os