diff --git a/tests/data/i_small2/i_small2.txt b/tests/data/i_small2/i_small2.txt
index 5741cd6..7d2b8cf 100644
--- a/tests/data/i_small2/i_small2.txt
+++ b/tests/data/i_small2/i_small2.txt
@@ -72,9 +72,9 @@ Study Protocol Type Term Source REF
 Study Protocol Description						
 Study Protocol URI						
 Study Protocol Version						
-Study Protocol Parameters Name						
-Study Protocol Parameters Name Term Accession Number						
-Study Protocol Parameters Name Term Source REF						
+Study Protocol Parameters Name	method;instrument					
+Study Protocol Parameters Name Term Accession Number	;					
+Study Protocol Parameters Name Term Source REF	;					
 Study Protocol Components Name						
 Study Protocol Components Type						
 Study Protocol Components Type Term Accession Number						
diff --git a/tests/test_modify_investigation.py b/tests/test_modify_investigation.py
new file mode 100644
index 0000000..8b9eae2
--- /dev/null
+++ b/tests/test_modify_investigation.py
@@ -0,0 +1,21 @@
+import pytest
+
+from altamisa.isatab import InvestigationForge
+
+
+def test_forge(assays_investigation_file):
+    # multiple studies
+    with pytest.raises(IndexError):
+        InvestigationForge(assays_investigation_file.name)
+
+
+def test_add_assay(small_investigation_file, small2_investigation_file, assays_investigation_file):
+    forge = InvestigationForge(small_investigation_file.name)
+    forge.add_assay(small2_investigation_file.name)
+    output = forge.investigation
+    assert len(output.studies[0].assays) == 2
+    assert len(output.studies[0].protocols) == 8
+
+    # multiple studies
+    with pytest.raises(IndexError):
+        forge.add_assay(assays_investigation_file.name)