diff --git a/tests/genomics/test_utils.py b/tests/genomics/test_utils.py
index 96c73add..5e1cf0f3 100644
--- a/tests/genomics/test_utils.py
+++ b/tests/genomics/test_utils.py
@@ -69,88 +69,69 @@ def test_generate_mappings_genome_id_bgc_id_empty_dir(tmp_path, caplog):
 
 
 @pytest.fixture
-def strain_collection() -> StrainCollection:
-    """Return a StrainCollection object."""
-    sc = StrainCollection()
-
-    strain = Strain("STRAIN_01")
-    strain.add_alias("BGC_01")
-    sc.add(strain)
-
-    strain = Strain("STRAIN_02")
-    strain.add_alias("BGC_02")
-    strain.add_alias("BGC_02_1")
-    sc.add(strain)
-
-    strain = Strain("SAMPLE_BGC_03")
-    sc.add(strain)
-
-    return sc
-
-
-@pytest.fixture
-def bgc_list() -> list[BGC]:
+def bgcs() -> list[BGC]:
     """Return a list of BGC objects."""
-    return [BGC("BGC_01", "NPR"), BGC("BGC_02", "Alkaloid"), BGC("SAMPLE_BGC_03", "Polyketide")]
-
-
-@pytest.fixture
-def gcf_list() -> list[GCF]:
-    """Return a list of GCF objects."""
-    gcf1 = GCF("1")
-    gcf1.bgc_ids |= {"BGC_01"}
-    gcf2 = GCF("2")
-    gcf2.bgc_ids |= {"BGC_02", "SAMPLE_BGC_03"}
-    return [gcf1, gcf2]
-
-
-@pytest.fixture
-def gcf_list_error() -> list[GCF]:
-    """Return a list of GCF objects for testing errors."""
-    gcf1 = GCF("1")
-    gcf1.bgc_ids |= {"SAMPLE_BGC_03", "BGC_04"}
-    return [gcf1]
+    return [BGC("BGC_01", "NPR"), BGC("BGC_02", "Alkaloid"), BGC("BGC_03", "Polyketide")]
 
 
-def test_add_strain_to_bgc(strain_collection, bgc_list):
+def test_add_strain_to_bgc(bgcs):
     """Test add_strain_to_bgc function."""
-    for bgc in bgc_list:
-        assert bgc.strain is None
-    add_strain_to_bgc(strain_collection, bgc_list)
-    for bgc in bgc_list:
-        assert bgc.strain is not None
-    assert bgc_list[0].strain.id == "STRAIN_01"
-    assert bgc_list[1].strain.id == "STRAIN_02"
-    assert bgc_list[2].strain.id == "SAMPLE_BGC_03"
-
-
-def test_add_strain_to_bgc_error(strain_collection):
+    strain1 = Strain("STRAIN_01")
+    strain1.add_alias("BGC_01")
+    strain2 = Strain("STRAIN_02")
+    strain2.add_alias("BGC_02")
+    strain2.add_alias("BGC_02_1")
+    strain3 = Strain("STRAIN_03")
+    strains = StrainCollection()
+    strains.add(strain1)
+    strains.add(strain2)
+    strains.add(strain3)
+
+    bgc_with_strain, bgc_without_strain = add_strain_to_bgc(strains, bgcs)
+
+    assert len(bgc_with_strain) == 2
+    assert len(bgc_without_strain) == 1
+    assert bgc_with_strain == [bgcs[0], bgcs[1]]
+    assert bgc_without_strain == [bgcs[2]]
+    assert bgc_with_strain[0].strain == strain1
+    assert bgc_with_strain[1].strain == strain2
+    assert bgc_without_strain[0].strain is None
+
+
+def test_add_strain_to_bgc_error(bgcs):
     """Test add_strain_to_bgc function error."""
-    bgcs = [BGC("BGC_04", "NPR")]
+    strain1 = Strain("STRAIN_01")
+    strain1.add_alias("BGC_01")
+    strain2 = Strain("STRAIN_02")
+    strain2.add_alias("BGC_01")
+    strains = StrainCollection()
+    strains.add(strain1)
+    strains.add(strain2)
+
     with pytest.raises(ValueError) as e:
-        add_strain_to_bgc(strain_collection, bgcs)
-    assert "Strain id 'BGC_04' from BGC object 'BGC_04' not found" in e.value.args[0]
+        add_strain_to_bgc(strains, bgcs)
+
+    assert "Multiple strain objects found for BGC id 'BGC_01'" in e.value.args[0]
 
 
-def test_add_bgc_to_gcf(bgc_list, gcf_list):
+def test_add_bgc_to_gcf(bgcs):
     """Test add_bgc_to_gcf function."""
-    assert gcf_list[0].bgc_ids == {"BGC_01"}
-    assert gcf_list[1].bgc_ids == {"BGC_02", "SAMPLE_BGC_03"}
-    assert len(gcf_list[0].bgcs) == 0
-    assert len(gcf_list[1].bgcs) == 0
-    add_bgc_to_gcf(bgc_list, gcf_list)
-    assert gcf_list[0].bgc_ids == {"BGC_01"}
-    assert gcf_list[1].bgc_ids == {"BGC_02", "SAMPLE_BGC_03"}
-    assert len(gcf_list[0].bgcs) == 1
-    assert len(gcf_list[1].bgcs) == 2
-    assert gcf_list[0].bgcs == set(bgc_list[:1])
-    assert gcf_list[1].bgcs == set(bgc_list[1:])
-
-
-def test_add_bgc_to_gcf_error(bgc_list, gcf_list_error):
-    """Test add_bgc_to_gcf function error."""
-    assert gcf_list_error[0].bgc_ids == {"SAMPLE_BGC_03", "BGC_04"}
-    assert len(gcf_list_error[0].bgcs) == 0
-    with pytest.raises(KeyError) as e:
-        add_bgc_to_gcf(bgc_list, gcf_list_error)
-    assert "BGC id 'BGC_04' from GCF object '1' not found" in e.value.args[0]
+    gcf1 = GCF("1")
+    gcf1.bgc_ids = {"BGC_01", "BGC_02"}
+    gcf2 = GCF("2")
+    gcf2.bgc_ids = {"BGC_03", "BGC_missing_01"}
+    gcf3 = GCF("3")
+    gcf3.bgc_ids = {"BGC_missing_02", "BGC_missing_03"}
+    gcfs = [gcf1, gcf2, gcf3]
+
+    gcf_with_bgc, gcf_without_bgc, gcf_missing_bgc = add_bgc_to_gcf(bgcs, gcfs)
+
+    assert len(gcf_with_bgc) == 2
+    assert len(gcf_without_bgc) == 1
+    assert len(gcf_missing_bgc) == 2
+    assert gcf_with_bgc == [gcf1, gcf2]
+    assert gcf_without_bgc == [gcf3]
+    assert gcf_missing_bgc == {gcf2: {"BGC_missing_01"}, gcf3: {"BGC_missing_02", "BGC_missing_03"}}
+    assert gcf_with_bgc[0].bgcs == {bgcs[0], bgcs[1]}
+    assert gcf_with_bgc[1].bgcs == {bgcs[2]}
+    assert gcf_without_bgc[0].bgcs == set()