diff --git a/dfschema/core/core.py b/dfschema/core/core.py
index 72ab9cb..5e3dfda 100644
--- a/dfschema/core/core.py
+++ b/dfschema/core/core.py
@@ -224,7 +224,7 @@ def to_file(self, path: Union[str, Path]) -> None:
                     import yaml
 
                     with path.open("w") as f:
-                        yaml.dump(schema_dict, f)
+                        yaml.dump(schema_dict, f, default_flow_style=False)
                 except ImportError:
                     raise ImportError("PyYaml is required to load yaml files")
             else:
diff --git a/dfschema/core/generate.py b/dfschema/core/generate.py
index 3948c38..8d9ade2 100644
--- a/dfschema/core/generate.py
+++ b/dfschema/core/generate.py
@@ -15,7 +15,9 @@ def generate_schema_dict_from_df(df: pd.DataFrame) -> dict:
         cd["dtype"] = (
             "string" if pd.api.types.is_string_dtype(df[col]) else str(df[col].dtype)
         )
-        cd["na_pct_below"] = max(0.01, (df[col].isnull().mean() + 0.1))  # +10%
+        cd["na_pct_below"] = min(
+            max(0.01, float(df[col].isnull().mean() + 0.1)), 1.0
+        )  # +10%
 
         if pd.api.types.is_numeric_dtype(df[col]):
             add_range = 0.05 * df[col].std()
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 8802a68..82d4879 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -53,18 +53,20 @@ def test_cli_validate_error():
 
 
 def test_cli_update():
+    from tempfile import TemporaryDirectory
     from dfschema.cli import app
     from dfschema.core.config import CURRENT_PROTOCOL_VERSION
 
-    output_path = "active_sales_v2.json"
-    result = runner.invoke(
-        app,
-        [
-            "update",
-            "tests/test_schemas/v1/good/active_sales.json",
-            output_path,
-        ],
-    )
+    with TemporaryDirectory() as tmpdirname:
+        output_path = f"{tmpdirname}/active_sales_v2.json"
+        result = runner.invoke(
+            app,
+            [
+                "update",
+                "tests/test_schemas/v1/good/active_sales.json",
+                output_path,
+            ],
+        )
 
     assert result.exit_code == 0, result.stdout
 
diff --git a/tests/test_read_write.py b/tests/test_read_write.py
index 93f310b..b0d797c 100644
--- a/tests/test_read_write.py
+++ b/tests/test_read_write.py
@@ -31,7 +31,7 @@ def test_write_schema_file(format, sample_df):
     from dfschema import DfSchema
     from tempfile import TemporaryDirectory
 
-    schema = DfSchema.from_df(sample_df)
+    schema: DfSchema = DfSchema.from_df(sample_df)  # type: ignore
 
     # create a temporary directory using the context manager
     with TemporaryDirectory() as tmpdirname:
@@ -44,7 +44,10 @@ def test_write_schema_file(format, sample_df):
         if format == "yml":
             import yaml
 
-            schema_structure = yaml.safe_load(txt)
+            try:
+                schema_structure = yaml.safe_load(txt)
+            except Exception as e:
+                raise Exception(txt) from e
         elif format == "json":
             import json