Add examples how to depend on all instances of a parametrized test.

Related to Issue #9.

doc/examples/all_params.py

@@ -0,0 +1,55 @@
+import pytest
+
+def instances(name, params):
+    def vstr(val):
+        if isinstance(val, (list, tuple)):
+            return "-".join([str(v) for v in val])
+        else:
+            return str(val)
+    return ["%s[%s]" % (name, vstr(v)) for v in params]
+
+
+params_a = range(17)
+
+@pytest.mark.parametrize("x", params_a)
+@pytest.mark.dependency()
+def test_a(x):
+    if x == 13:
+        pytest.xfail("deliberate fail")
+        assert False
+    else:
+        pass
+
+@pytest.mark.dependency(depends=instances("test_a", params_a))
+def test_b():
+    pass
+
+params_c = zip(range(0,8,2), range(2,6))
+
+@pytest.mark.parametrize("x,y", params_c)
+@pytest.mark.dependency()
+def test_c(x, y):
+    if x > y:
+        pytest.xfail("deliberate fail")
+        assert False
+    else:
+        pass
+
+@pytest.mark.dependency(depends=instances("test_c", params_c))
+def test_d():
+    pass
+
+params_e = ['abc', 'def']
+
+@pytest.mark.parametrize("s", params_e)
+@pytest.mark.dependency()
+def test_e(s):
+    if 'e' in s:
+        pytest.xfail("deliberate fail")
+        assert False
+    else:
+        pass
+
+@pytest.mark.dependency(depends=instances("test_e", params_e))
+def test_f():
+    pass

doc/src/advanced.rst

@@ -52,3 +52,30 @@ In this example, both `test_b[7]` and `test_c[7]` are skipped, because
 `test_a[7]` deliberately fails.
 
 .. __: https://docs.pytest.org/en/latest/fixture.html#automatic-grouping-of-tests-by-fixture-instances
+
+Depend on all instances of a parametrized test at once
+------------------------------------------------------
+
+If a test depends on a all instances of a parametrized test at once,
+listing all of them in the :func:`pytest.mark.dependency` marker
+explicitly might not be the best solution.  But you can dynamically
+compile these lists from the parameter values, as in the following
+example:
+
+.. literalinclude:: ../examples/all_params.py
+
+Here, `test_b`, `test_d`, and `test_f` will be skipped because they
+depend on all instances of `test_a`, `test_c`, and `test_e`
+respectively, but `test_a[13]`, `test_c[6-5]`, and `test_e[def]` fail.
+The list of the test instances is compiled in the helper function
+`instances()`.
+
+Unfortunately you need knowledge how pytest encodes parameter values
+in test instance names to write this helper function.  Note in
+particular how lists of parameter values are compiled into one single
+string in the case of multi parameter tests.  But also note that this
+example of the `instances()` helper will only work for simple cases.
+It requires the parameter values to be scalars that can easily be
+converted to strings.  And it will fail if the same list of parameters
+is passed to the same test more then once, because then, pytest will
+add an index to the name to disambiguate the parameter values.