Ignore expected warnings during testing (quantumlib#1065)

A few test cases produce `RuntimeWarning`'s. These turn out to be
expected. We can indicate to pytest that they can be ignored.

Author: mhucka

src/openfermion/linalg/davidson_test.py

@@ -14,6 +14,7 @@
 import logging
 import unittest
 
+import pytest
 import numpy
 import numpy.linalg
 import scipy.linalg
@@ -406,9 +407,10 @@ def test_get_lowest_z_real(self):
         initial_guess = 1.0j * numpy.random.rand(dimension, n_lowest)
         numpy.random.seed(dimension * 2)
         initial_guess += numpy.random.rand(dimension, n_lowest)
-        success, eigen_values, eigen_vectors = davidson.get_lowest_n(
-            n_lowest, initial_guess, max_iterations=10
-        )
+        with pytest.warns(RuntimeWarning):
+            success, eigen_values, eigen_vectors = davidson.get_lowest_n(
+                n_lowest, initial_guess, max_iterations=10
+            )
 
         # one half of the eigenvalues is -1 and the other half is +1, together
         # with the coefficient.
@@ -436,9 +438,13 @@ def test_get_lowest_y_real_fail(self):
         initial_guess = 1.0j * numpy.random.rand(dimension, n_lowest)
         numpy.random.seed(dimension * 2)
         initial_guess += numpy.random.rand(dimension, n_lowest)
-        success, _, eigen_vectors = davidson.get_lowest_n(
-            n_lowest, initial_guess, max_iterations=10
-        )
+        with pytest.warns(
+            RuntimeWarning,
+            match=("Unable to get real only eigenvectors|Initial guess is not real only!"),
+        ):
+            success, _, eigen_vectors = davidson.get_lowest_n(
+                n_lowest, initial_guess, max_iterations=10
+            )
 
         self.assertFalse(success)
 
@@ -458,9 +464,13 @@ def test_get_lowest_y_real(self):
         initial_guess = 1.0j * numpy.random.rand(dimension, n_lowest)
         numpy.random.seed(dimension * 2)
         initial_guess += numpy.random.rand(dimension, n_lowest)
-        success, eigen_values, eigen_vectors = davidson.get_lowest_n(
-            n_lowest, initial_guess, max_iterations=10
-        )
+        with pytest.warns(
+            RuntimeWarning,
+            match=("Unable to get real only eigenvectors|Initial guess is not real only!"),
+        ):
+            success, eigen_values, eigen_vectors = davidson.get_lowest_n(
+                n_lowest, initial_guess, max_iterations=10
+            )
 
         # one half of the eigenvalues is -1 and the other half is +1, together
         # with the coefficient.
@@ -487,9 +497,13 @@ def test_get_lowest_y_complex(self):
         initial_guess = 1.0j * numpy.random.rand(dimension, n_lowest)
         numpy.random.seed(dimension * 2)
         initial_guess += numpy.random.rand(dimension, n_lowest)
-        success, eigen_values, eigen_vectors = davidson.get_lowest_n(
-            n_lowest, initial_guess, max_iterations=10
-        )
+        with pytest.warns(
+            RuntimeWarning,
+            match=("Unable to get real only eigenvectors|Initial guess is not real only!"),
+        ):
+            success, eigen_values, eigen_vectors = davidson.get_lowest_n(
+                n_lowest, initial_guess, max_iterations=10
+            )
 
         # one half of the eigenvalues is -1 and the other half is +1, together
         # with the coefficient.
@@ -658,7 +672,8 @@ def test_append_vectors_big_col(self):
         """Test append_random_vectors() with too many failed trial."""
         row = 10
         vectors = numpy.eye(row, row)
-        new_vectors = append_random_vectors(vectors, 1)
+        with pytest.warns(RuntimeWarning):
+            new_vectors = append_random_vectors(vectors, 1)
 
         self.assertTrue(numpy.allclose(new_vectors, vectors))
 

src/openfermion/ops/operators/qubit_operator_test.py

@@ -231,7 +231,9 @@ def check_sum(operators, operator):
 def test_get_operator_groups_zero():
     """Tests get_operator_groups() with one group."""
     operator = generate_operator(0, 20)
-    operator_groups = list(operator.get_operator_groups(0))
+    with pytest.warns(RuntimeWarning, match="Invalid num_groups 0 < 1"):
+        # Min. is 1; get_operator_groups() should issue warning and use 1.
+        operator_groups = list(operator.get_operator_groups(0))
 
     # Using 1 group instead.
     assert check_length(operator_groups, [20])