Add multiply_scenarios

3 files changed, 68 insertions, 0 deletions

diff --git a/README b/README
index 14df2e1..bf49b4b 100644
--- a/README
+++ b/README
@@ -267,3 +267,16 @@ Advice on Writing Scenarios
 
 If a parameterised test is because of a bug run without being parameterized,
 it should fail rather than running with defaults, because this can hide bugs.
+
+
+Producing Scenarios
+===================
+
+The `multiply_scenarios` function produces the cross-product of the scenarios
+passed in::
+
+    scenarios = multiply_scenarios(
+	vary_by_http_client(),
+	vary_by_http_protocol_version(),
+	)
+  
diff --git a/lib/testscenarios/scenarios.py b/lib/testscenarios/scenarios.py
index 3cf8091..c284afd 100644
--- a/lib/testscenarios/scenarios.py
+++ b/lib/testscenarios/scenarios.py
@@ -22,6 +22,11 @@ __all__ = [
     'load_tests_apply_scenarios',
     ]
 
+
+from itertools import (
+    chain,
+    product,
+    )
 import unittest
 
 from testtools.testcase import clone_test_with_new_id
@@ -104,3 +109,23 @@ def load_tests_apply_scenarios(*params):
     result = loader.suiteClass()
     result.addTests(generate_scenarios(standard_tests))
     return result
+
+
+def multiply_scenarios(*scenarios):
+    """Multiply two or more iterables of scenarios.
+
+    It is safe to pass scenario generators or iterators.
+
+    :returns: A list of compound scenarios: the cross-product of all 
+        scenarios, with the names concatenated and the parameters
+        merged together.
+    """
+    r = []
+    scenario_lists = map(list, scenarios)
+    products = product(*scenario_lists)
+    for combo in products:
+        names, params = zip(*combo)
+        for p in params:
+            d.update(p.iteritems())
+        r.append((','.join(names), d))
+    return r
diff --git a/lib/testscenarios/tests/test_scenarios.py b/lib/testscenarios/tests/test_scenarios.py
index 97a2a6b..ecba25c 100644
--- a/lib/testscenarios/tests/test_scenarios.py
+++ b/lib/testscenarios/tests/test_scenarios.py
@@ -23,6 +23,7 @@ from testscenarios.scenarios import (
     apply_scenarios,
     generate_scenarios,
     load_tests_apply_scenarios,
+    multiply_scenarios,
     )
 import testtools
 from testtools.tests.helpers import LoggingResult
@@ -211,3 +212,32 @@ class TestLoadTests(testtools.TestCase):
             2,
             len(result_tests),
             result_tests)
+
+
+class TestMultiplyScenarios(testtools.TestCase):
+
+    def test_multiply_scenarios(self):
+        def s(name):
+            for i in 'ab':
+                yield i, {name: i}
+        r = list(multiply_scenarios(s('p'), s('q')))
+        self.assertEquals([
+            ('a,a', dict(p='a', q='a')),
+            ('a,b', dict(p='a', q='b')),
+            ('b,a', dict(p='b', q='a')),
+            ('b,b', dict(p='b', q='b')),
+            ],
+            r)
+
+    def test_multiply_many_scenarios(self):
+        def s(name):
+            for i in 'abc':
+                yield i, {name: i}
+        r = list(multiply_scenarios(s('p'), s('q'), s('r'), s('t')))
+        self.assertEqual(
+            3**4,
+            len(r),
+            r)
+        self.assertEqual(
+            'a,a,a,a',
+            r[0][0])