diff --git a/graphblas/core/ss/config.py b/graphblas/core/ss/config.py
index 70a7dd196..e1ccd15a0 100644
--- a/graphblas/core/ss/config.py
+++ b/graphblas/core/ss/config.py
@@ -210,5 +210,5 @@ def __repr__(self):
             + "})"
         )
 
-    def _ipython_key_completions_(self):  # pragma: no cover (ipython)
+    def _ipython_key_completions_(self):
         return list(self)
diff --git a/graphblas/tests/test_io.py b/graphblas/tests/test_io.py
index d2e57cebe..e5eb0020d 100644
--- a/graphblas/tests/test_io.py
+++ b/graphblas/tests/test_io.py
@@ -192,6 +192,41 @@ def test_from_networkx_rejects_array_weights(graph_cls):
         gb.io.from_networkx(G)
 
 
+@pytest.mark.skipif("not nx or not ss")
+@pytest.mark.parametrize(
+    "graph_cls", [nx.Graph, nx.DiGraph, nx.MultiGraph, nx.MultiDiGraph] if nx else []
+)
+def test_from_networkx_rejects_string_weights(graph_cls):
+    # String weights infer a 1-D <U array, so a shape test alone would let them
+    # through; only the dtype-kind half of the guard sends these to scipy, which
+    # rejects them the way it always has.
+    G = graph_cls()
+    G.add_edge(0, 1, weight="a")
+    G.add_edge(1, 2, weight="b")
+    with pytest.raises(ValueError, match="does not support dtype"):
+        gb.io.from_networkx(G)
+
+
+@pytest.mark.skipif("not nx")
+def test_from_networkx_unsupported_dtype_is_valueerror(monkeypatch):
+    # scipy < 1.15 builds a string-dtype coo array happily and only fails converting
+    # it to csr, and networkx re-raises that failure as a NetworkXError blaming the
+    # sparse format. from_networkx restates it as the ValueError newer scipy raises
+    # directly, which is what the caller can act on; monkeypatching the fallback
+    # exercises the old behavior on any scipy.
+    import graphblas.io._networkx as _gnx
+
+    def _raise_networkx_error(*args, **kwargs):
+        raise nx.NetworkXError("Unknown sparse matrix format: csr")
+
+    monkeypatch.setattr(_gnx, "_from_networkx_via_scipy", _raise_networkx_error)
+    G = nx.Graph()
+    G.add_edge(0, 1, weight="a")
+    G.add_edge(1, 2, weight="b")
+    with pytest.raises(ValueError, match="does not support dtype"):
+        gb.io.from_networkx(G)
+
+
 @pytest.mark.skipif("not nx or not ss")
 @pytest.mark.parametrize(
     "graph_cls", [nx.Graph, nx.DiGraph, nx.MultiGraph, nx.MultiDiGraph] if nx else []
@@ -460,6 +495,24 @@ def test_matrix_market_bad_engine():
         gb.io.mmread(mm_out, engine="bad_engine")
 
 
+@pytest.mark.skipif("not ss")
+@pytest.mark.skipif("fmm is not None")
+def test_matrix_market_fmm_engine_unavailable():
+    # Naming the deprecated engine warns before anything else, so the caller hears
+    # about the deprecation even when the install that would satisfy it is missing.
+    A = gb.Matrix.from_coo([0, 0, 3, 5], [1, 4, 0, 2], [1, 0, 2, -1], nrows=7, ncols=6)
+    with (
+        pytest.warns(DeprecationWarning, match="fast_matrix_market is no longer maintained"),
+        pytest.raises(ImportError, match="required to write Matrix Market files"),
+    ):
+        gb.io.mmwrite(BytesIO(), A, engine="fmm")
+    with (
+        pytest.warns(DeprecationWarning, match="fast_matrix_market is no longer maintained"),
+        pytest.raises(ImportError, match="required to read Matrix Market files"),
+    ):
+        gb.io.mmread(BytesIO(), engine="fast_matrix_market")
+
+
 @pytest.mark.skipif("not ss")
 def test_scipy_sparse():
     a = np.arange(12).reshape(3, 4)
diff --git a/graphblas/tests/test_ss_utils.py b/graphblas/tests/test_ss_utils.py
index 40774186c..72d3952a4 100644
--- a/graphblas/tests/test_ss_utils.py
+++ b/graphblas/tests/test_ss_utils.py
@@ -237,6 +237,22 @@ def test_global_config():
     assert "format" in repr(config)
 
 
+def test_global_config_key_completions():
+    # IPython offers these for `config[<tab>]`, so they must be the keys that
+    # actually resolve, not the attributes of the mapping object.
+    config = gb.ss.config
+    completions = config._ipython_key_completions_()
+    assert set(completions) == set(config._options)
+    for key in completions:
+        config[key]
+    # About aliases the same hook onto its own __iter__ (gb.ss.about[<tab>])
+    about = gb.ss.about
+    completions = about._ipython_key_completions_()
+    assert set(completions) == set(about)
+    for key in completions:
+        about[key]
+
+
 @pytest.mark.skipif("gb.core.ss._IS_SSGB7")
 def test_context():
     context = gb.ss.Context()