Make the test class instance behaviour clearer

In the "Getting Started" doc, the test class instance example for
instance sharing doesn't actually demonstrate anything about the
reinstantiation of the class. This change shows clearly how the instance
data isn't retained between test runs.

AUTHORS

@@ -62,6 +62,7 @@ Charles Machalow
 Charnjit SiNGH (CCSJ)
 Chris Lamb
 Chris NeJame
+Chris Rose
 Christian Boelsen
 Christian Fetzer
 Christian Neumüller

doc/en/getting-started.rst

@@ -169,40 +169,34 @@ This is outlined below:
 
     # content of test_class_demo.py
     class TestClassDemoInstance:
+        value = 0
+
         def test_one(self):
-            assert 0
+            self.value = 1
+            assert self.value == 1
 
         def test_two(self):
-            assert 0
+            assert self.value == 1
 
 
 .. code-block:: pytest
 
     $ pytest -k TestClassDemoInstance -q
-    FF                                                                   [100%]
+    .F                                                                   [100%]
     ================================= FAILURES =================================
-    ______________________ TestClassDemoInstance.test_one ______________________
-
-    self = <test_class_demo.TestClassDemoInstance object at 0xdeadbeef>
-
-        def test_one(self):
-    >       assert 0
-    E       assert 0
-
-    test_class_demo.py:3: AssertionError
     ______________________ TestClassDemoInstance.test_two ______________________
 
     self = <test_class_demo.TestClassDemoInstance object at 0xdeadbeef>
 
         def test_two(self):
-    >       assert 0
-    E       assert 0
+    >       assert self.value == 1
+    E       assert 0 == 1
+    E        +  where 0 = <test_class_demo.TestClassDemoInstance object at 0xdeadbeef>.value
 
-    test_class_demo.py:6: AssertionError
+    test_class_demo.py:9: AssertionError
     ========================= short test summary info ==========================
-    FAILED test_class_demo.py::TestClassDemoInstance::test_one - assert 0
-    FAILED test_class_demo.py::TestClassDemoInstance::test_two - assert 0
-    2 failed in 0.12s
+    FAILED test_class_demo.py::TestClassDemoInstance::test_two - assert 0 == 1
+    1 failed, 1 passed in 0.04s
 
 Note that attributes added at class level are *class attributes*, so they will be shared between tests.