Raise error messages when ask is called without ask_dqd (#338)

## Description

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## TODO

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accomplish. -->

## Questions

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## Status

- [x] I have read the guidelines in
[CONTRIBUTING.md](https://github.com/icaros-usc/pyribs/blob/master/CONTRIBUTING.md)
- [x] I have formatted my code using `yapf`
- [x] I have tested my code by running `pytest`
- [x] I have linted my code with `pylint`
- [x] I have added a one-line description of my change to the changelog
in `HISTORY.md`
- [x] This PR is ready to go

HISTORY.md

@@ -4,8 +4,13 @@
 
 ### Changelog
 
+#### API
+
+- Raise error messages when `ask` is called without `ask_dqd` (#338)
+
 #### Documentation
- - Add BibTex citation for GECCO 2023 (#337)
+
+- Add BibTex citation for GECCO 2023 (#337)
 
 ## 0.5.1
 

ribs/emitters/_gradient_arborescence_emitter.py

@@ -258,7 +258,14 @@ def ask(self):
         Returns:
             (:attr:`batch_size`, :attr:`solution_dim`) array -- a batch of new
             solutions to evaluate.
+        Raises:
+            RuntimeError: This method was called without first passing gradients
+                with calls to ask_dqd() and tell_dqd().
         """
+        if self._jacobian_batch is None:
+            raise RuntimeError("Please call ask_dqd() and tell_dqd() "
+                               "before calling ask().")
+
         coeff_lower_bounds = np.full(
             self._num_coefficients,
             -np.inf,
@@ -382,6 +389,9 @@ def tell(self,
                 floats represent, refer to :meth:`ribs.archives.add()`.
             metadata_batch (array-like): 1d object array containing a metadata
                 object for each solution.
+        Raises:
+            RuntimeError: This method was called without first passing gradients
+                with calls to ask_dqd() and tell_dqd().
         """
         # Preprocessing arguments.
         solution_batch = np.asarray(solution_batch)
@@ -403,7 +413,8 @@ def tell(self,
                             metadata_batch=metadata_batch)
 
         if self._jacobian_batch is None:
-            raise RuntimeError("tell() was called without calling tell_dqd().")
+            raise RuntimeError("Please call ask_dqd(), tell_dqd(), and ask() "
+                               "before calling tell().")
 
         # Increase iteration counter.
         self._itrs += 1

tests/emitters/gradient_arborescence_emitter_test.py

@@ -59,3 +59,25 @@ def test_bounds_must_be_none():
                                     normalize_grad=False,
                                     bounds=bound,
                                     batch_size=batch_size)
+
+
+def test_ask_dqd_must_be_called_before_ask():
+    archive = GridArchive(solution_dim=1, dims=[10], ranges=[(-1.0, 1.0)])
+    with pytest.raises(RuntimeError):
+        emitter = GradientArborescenceEmitter(archive,
+                                              x0=np.array([0]),
+                                              sigma0=1.0,
+                                              lr=1.0)
+        # Must call ask_dqd() before calling ask() to set the jacobian.
+        emitter.ask()
+
+
+def test_tell_dqd_must_be_called_before_tell():
+    archive = GridArchive(solution_dim=1, dims=[10], ranges=[(-1.0, 1.0)])
+    with pytest.raises(RuntimeError):
+        emitter = GradientArborescenceEmitter(archive,
+                                              x0=np.array([0]),
+                                              sigma0=1.0,
+                                              lr=1.0)
+        # Must call ask_dqd() before calling ask() to set the jacobian.
+        emitter.tell([[0]], [0], [[0]], [0], [0])