Add default_value to fidelity

Why:

The EVC is using the default_value to build adapters. Also this default
value can be used as a fall-back if the algorithms does not support
multi-fidelity optimization. This is handy is we want to try different
algorithms with the same experiment configuration.

src/orion/algo/space.py

@@ -670,6 +670,8 @@ class Fidelity(Dimension):
     ----------
     name : str
         Name of the dimension
+    default_value: int
+        Maximum of the fidelity interval.
 
     """
 
@@ -688,6 +690,11 @@ def __init__(self, name, low, high, base=2):
         self.prior = None
         self._prior_name = 'None'
 
+    @property
+    def default_value(self):
+        """Return `high`"""
+        return self.high
+
     def get_prior_string(self):
         """Build the string corresponding to current prior"""
         return 'fidelity({}, {}, {})'.format(self.low, self.high, self.base)
@@ -698,7 +705,7 @@ def validate(self):
 
     def sample(self, n_samples=1, seed=None):
         """Do not do anything."""
-        return ['fidelity']
+        return [self.high]
 
     def interval(self, alpha=1.0):
         """Do not do anything."""

tests/functional/branching/test_branching.py

@@ -454,9 +454,22 @@ def test_auto_resolution_does_resolve(init_full_x_full_y, monkeypatch):
     orion.core.cli.main(
         ("init_only -n {name} --branch {branch} ./black_box_with_y.py "
          "-x~uniform(0,10) "
-         "-w~choices(['a','b'],default_value='a')").format(name=name, branch=branch).split(" "))
-    orion.core.cli.main("insert -n {name} script -x=2 -w=b".format(name=branch).split(" "))
-    orion.core.cli.main("insert -n {name} script -x=1".format(name=branch).split(" "))
+         "-w~choices(['a','b'])").format(name=name, branch=branch).split(" "))
+
+
+def test_auto_resolution_with_fidelity(init_full_x_full_y, monkeypatch):
+    """Test that auto-resolution does resolve all conflicts including new fidelity"""
+    # Patch cmdloop to avoid autoresolution's prompt
+    monkeypatch.setattr('sys.__stdin__.isatty', lambda: True)
+
+    name = "full_x_full_y"
+    branch = "half_x_no_y_new_w"
+    # If autoresolution was not succesfull, this to fail with a sys.exit without registering the
+    # experiment
+    orion.core.cli.main(
+        ("init_only -n {name} --branch {branch} ./black_box_with_y.py "
+         "-x~uniform(0,10) "
+         "-w~fidelity(1,10)").format(name=name, branch=branch).split(" "))
 
 
 def test_init_w_version_from_parent_w_children(clean_db, monkeypatch):

tests/unittests/algo/test_space.py

@@ -528,10 +528,18 @@ def test_base(self):
         assert "Base should be greater than 1" == str(exc.value)
 
     def test_sampling(self):
-        """Make sure Fidelity simply returns `fidelity`"""
+        """Make sure Fidelity simply returns `high`"""
         dim = Fidelity('epoch', 1, 2)
+        assert dim.sample() == [2]
+        dim = Fidelity('epoch', 1, 5)
+        assert dim.sample() == [5]
 
-        assert dim.sample() == ['fidelity']
+    def test_default_value(self):
+        """Make sure Fidelity simply returns `high`"""
+        dim = Fidelity('epoch', 1, 2)
+        assert dim.default_value == 2
+        dim = Fidelity('epoch', 1, 5)
+        assert dim.default_value == 5
 
     def test_contains(self):
         """Make sure fidelity.__contains__ tests based on (min, max)"""