Add tests

tests/test_core.py

@@ -84,6 +84,14 @@ a;b;c"""
     assert report.valid
 
 
+def test_empty_required_value(schema_abc):
+    source = [["A", "B", "C"], ["", "b", "c"]]
+    report = validate(source, schema_abc)
+    assert not report.valid
+    assert len(report["tasks"][0]["errors"]) == 1
+    assert report["tasks"][0]["errors"][0]["code"] == "constraint-error"
+
+
 def test_missing_required_column(schema_abc):
     source = [["B", "C"], ["b", "c"]]
     report = validate(source, schema_abc)