generalize skipping

- rename pytest_xfail to pytest_skip
- dynamic "skipif" and "xfail" decorators
- move most skipping code to the plugin

also coming with this commit:
- extend mark keyword to accept positional args + docs
- fix a few documentation related issues
- leave version as "trunk" for now

--HG--
branch : trunk

testing/pytest/plugin/test_pytest_skipping.py

@@ -0,0 +1,109 @@
+import py
+
+def test_xfail_decorator(testdir):
+    p = testdir.makepyfile(test_one="""
+        import py
+        @py.test.mark.xfail
+        def test_this():
+            assert 0
+
+        @py.test.mark.xfail
+        def test_that():
+            assert 1
+    """)
+    result = testdir.runpytest(p)
+    extra = result.stdout.fnmatch_lines([
+        "*expected failures*",
+        "*test_one.test_this*test_one.py:4*",
+        "*UNEXPECTEDLY PASSING*",
+        "*test_that*",
+        "*1 xfailed*"
+    ])
+    assert result.ret == 1
+
+def test_skipif_decorator(testdir):
+    p = testdir.makepyfile("""
+        import py
+        @py.test.mark.skipif("hasattr(sys, 'platform')")
+        def test_that():
+            assert 0
+    """)
+    result = testdir.runpytest(p)
+    extra = result.stdout.fnmatch_lines([
+        "*Skipped*platform*",
+        "*1 skipped*"
+    ])
+    assert result.ret == 0
+
+def test_skipif_class(testdir):
+    p = testdir.makepyfile("""
+        import py
+        class TestClass:
+            skipif = "True"
+            def test_that(self):
+                assert 0
+            def test_though(self):
+                assert 0
+    """)
+    result = testdir.runpytest(p)
+    extra = result.stdout.fnmatch_lines([
+        "*2 skipped*"
+    ])
+
+def test_getexpression(testdir):
+    from _py.test.plugin.pytest_skipping import getexpression
+    l = testdir.getitems("""
+        import py
+        mod = 5
+        class TestClass:
+            cls = 4
+            @py.test.mark.func(3)
+            def test_func(self):
+                pass
+            @py.test.mark.just
+            def test_other(self):
+                pass
+    """)
+    item, item2 = l
+    assert getexpression(item, 'xyz') is None
+    assert getexpression(item, 'func') == 3
+    assert getexpression(item, 'cls') == 4
+    assert getexpression(item, 'mod') == 5
+
+    assert getexpression(item2, 'just')
+
+def test_evalexpression_cls_config_example(testdir):
+    from _py.test.plugin.pytest_skipping import evalexpression
+    item, = testdir.getitems("""
+        class TestClass:
+            skipif = "config._hackxyz"
+            def test_func(self):
+                pass
+    """)
+    item.config._hackxyz = 3
+    x, y = evalexpression(item, 'skipif')
+    assert x == 'config._hackxyz'
+    assert y == 3
+
+def test_importorskip():
+    from _py.test.outcome import Skipped
+    from _py.test.plugin.pytest_skipping import importorskip
+    assert importorskip == py.test.importorskip
+    try:
+        sys = importorskip("sys")
+        assert sys == py.std.sys
+        #path = py.test.importorskip("os.path")
+        #assert path == py.std.os.path
+        py.test.raises(Skipped, "py.test.importorskip('alskdj')")
+        py.test.raises(SyntaxError, "py.test.importorskip('x y z')")
+        py.test.raises(SyntaxError, "py.test.importorskip('x=y')")
+        path = importorskip("py", minversion=".".join(py.__version__))
+        mod = py.std.types.ModuleType("hello123")
+        mod.__version__ = "1.3"
+        py.test.raises(Skipped, """
+            py.test.importorskip("hello123", minversion="5.0")
+        """)
+    except Skipped:
+        print(py.code.ExceptionInfo())
+        py.test.fail("spurious skip")
+