diff --git a/mne/channels/tests/test_unify_bads.py b/mne/channels/tests/test_unify_bads.py
new file mode 100644
index 00000000000..ac04983802b
--- /dev/null
+++ b/mne/channels/tests/test_unify_bads.py
@@ -0,0 +1,53 @@
+import pytest
+from mne.channels import unify_bad_channels
+
+
+def test_error_raising(raw, epochs):
+    """Tests input checking."""
+    with pytest.raises(TypeError, match=r"must be an instance of list"):
+        unify_bad_channels("bad input")
+    with pytest.raises(ValueError, match=r"insts must not be empty"):
+        unify_bad_channels([])
+    with pytest.raises(TypeError, match=r"each object in insts must be an instance of"):
+        unify_bad_channels(["bad_instance"])
+    with pytest.raises(ValueError, match=r"same type"):
+        unify_bad_channels([raw, epochs])
+    with pytest.raises(ValueError, match=r"Channels do not match across"):
+        raw_alt1 = raw.copy()
+        raw_alt1.drop_channels(raw.info["ch_names"][-1])
+        unify_bad_channels([raw, raw_alt1])  # ch diff preserving order
+    with pytest.raises(ValueError, match=r"sorted differently"):
+        raw_alt2 = raw.copy()
+        new_order = [raw.ch_names[-1]] + raw.ch_names[:-1]
+        raw_alt2.reorder_channels(new_order)
+        unify_bad_channels([raw, raw_alt2])
+
+
+def test_bads_compilation(raw):
+    """Tests that bads are compiled properly.
+
+    Tests two cases: a) single instance passed to function with an existing
+    bad, and b) multiple instances passed to function with varying compilation
+    scenarios including empty bads, unique bads, and partially duplicated bads
+    listed out-of-order.
+
+    Only the Raw instance type is tested, since bad channel implementation is
+    controlled across instance types with a MixIn class.
+    """
+    assert raw.info["bads"] == []
+    chns = raw.ch_names[:3]
+    no_bad = raw.copy()
+    one_bad = raw.copy()
+    one_bad.info["bads"] = [chns[1]]
+    three_bad = raw.copy()
+    three_bad.info["bads"] = chns
+    # scenario 1: single instance passed with actual bads
+    s_out = unify_bad_channels([one_bad])
+    assert len(s_out) == 1, len(s_out)
+    assert s_out[0].info["bads"] == [chns[1]], (s_out[0].info["bads"], chns[1])
+    # scenario 2: multiple instances passed
+    m_out = unify_bad_channels([one_bad, no_bad, three_bad])
+    assert len(m_out) == 3, len(m_out)
+    expected_order = [chns[1], chns[0], chns[2]]
+    for inst in m_out:
+        assert inst.info["bads"] == expected_order