Abort operations if their dependencies fail

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>

tests/unit/parallel_test.py

@@ -0,0 +1,73 @@
+from __future__ import absolute_import
+from __future__ import unicode_literals
+
+import six
+from docker.errors import APIError
+
+from compose.parallel import parallel_execute
+
+
+web = 'web'
+db = 'db'
+data_volume = 'data_volume'
+cache = 'cache'
+
+objects = [web, db, data_volume, cache]
+
+deps = {
+    web: [db, cache],
+    db: [data_volume],
+    data_volume: [],
+    cache: [],
+}
+
+
+def test_parallel_execute():
+    results = parallel_execute(
+        objects=[1, 2, 3, 4, 5],
+        func=lambda x: x * 2,
+        get_name=six.text_type,
+        msg="Doubling",
+    )
+
+    assert sorted(results) == [2, 4, 6, 8, 10]
+
+
+def test_parallel_execute_with_deps():
+    log = []
+
+    def process(x):
+        log.append(x)
+
+    parallel_execute(
+        objects=objects,
+        func=process,
+        get_name=lambda obj: obj,
+        msg="Processing",
+        get_deps=lambda obj: deps[obj],
+    )
+
+    assert sorted(log) == sorted(objects)
+
+    assert log.index(data_volume) < log.index(db)
+    assert log.index(db) < log.index(web)
+    assert log.index(cache) < log.index(web)
+
+
+def test_parallel_execute_with_upstream_errors():
+    log = []
+
+    def process(x):
+        if x is data_volume:
+            raise APIError(None, None, "Something went wrong")
+        log.append(x)
+
+    parallel_execute(
+        objects=objects,
+        func=process,
+        get_name=lambda obj: obj,
+        msg="Processing",
+        get_deps=lambda obj: deps[obj],
+    )
+
+    assert log == [cache]