Improve error message when cores or memory is not specified (#331)

dask_jobqueue/core.py

@@ -203,14 +203,12 @@ def __init__(
         if shebang is None:
             shebang = dask.config.get("jobqueue.%s.shebang" % config_name)
 
-        if cores is None:
-            raise ValueError(
-                "You must specify how many cores to use per job like ``cores=8``"
-            )
-
-        if memory is None:
+        if cores is None or memory is None:
             raise ValueError(
-                "You must specify how much memory to use per job like ``memory='24 GB'``"
+                "You must specify how much cores and memory per job you want to use, for example:\n"
+                "cluster = {}(cores={}, memory={!r})".format(
+                    self.__class__.__name__, cores or 8, memory or "24GB"
+                )
             )
 
         # This attribute should be overridden

dask_jobqueue/tests/test_jobqueue_core.py

@@ -173,3 +173,19 @@ def test_jobqueue_cluster_call(tmpdir):
     match = re.compile(match, re.DOTALL)
     with pytest.raises(RuntimeError, match=match):
         cluster._call([sys.executable, path_with_error.strpath])
+
+
+@pytest.mark.parametrize(
+    "Cluster",
+    [PBSCluster, MoabCluster, SLURMCluster, SGECluster, LSFCluster, OARCluster],
+)
+def test_cluster_has_cores_and_memory(Cluster):
+    cls_name = Cluster.__name__ + r"\("
+    with pytest.raises(ValueError, match=cls_name + r"cores=\d, memory='\d+GB'"):
+        Cluster()
+
+    with pytest.raises(ValueError, match=cls_name + r"cores=\d, memory='1GB'"):
+        Cluster(memory="1GB")
+
+    with pytest.raises(ValueError, match=cls_name + r"cores=4, memory='\d+GB'"):
+        Cluster(cores=4)