diff --git a/test/test_label.py b/test/test_label.py
new file mode 100644
index 0000000..fe53f1b
--- /dev/null
+++ b/test/test_label.py
@@ -0,0 +1,43 @@
+"""
+Author: Sergey Vartanov (me@enzet.ru).
+"""
+from typing import List
+
+from roentgen.scheme import Scheme
+from roentgen.text import Label
+
+
+def construct_labels(tags) -> List[Label]:
+    """
+    Construct labels from OSM node tags.
+    """
+    scheme = Scheme("scheme/default.yml")
+    return scheme.construct_text(tags, True)
+
+
+def test_1_label() -> None:
+    """
+    Test tags that should be converted into single label.
+    """
+    labels = construct_labels({"name": "Name"})
+    assert len(labels) == 1
+    assert labels[0].text == "Name"
+
+
+def test_1_label_unknown_tags() -> None:
+    """
+    Test tags with some unknown tags that should be converted into single label.
+    """
+    labels = construct_labels({"name": "Name", "aaa": "bbb"})
+    assert len(labels) == 1
+    assert labels[0].text == "Name"
+
+
+def test_2_labels() -> None:
+    """
+    Test tags that should be converted into two labels.
+    """
+    labels = construct_labels({"name": "Name", "ref": "5"})
+    assert len(labels) == 2
+    assert labels[0].text == "Name"
+    assert labels[1].text == "5"
diff --git a/test/test_text.py b/test/test_text.py
index fe53f1b..d425cac 100644
--- a/test/test_text.py
+++ b/test/test_text.py
@@ -1,43 +1,14 @@
 """
+Test text generation.
+
 Author: Sergey Vartanov (me@enzet.ru).
 """
-from typing import List
-
-from roentgen.scheme import Scheme
-from roentgen.text import Label
+from roentgen.text import format_voltage
 
 
-def construct_labels(tags) -> List[Label]:
+def test_voltage() -> None:
     """
-    Construct labels from OSM node tags.
+    Test voltage tag value processing.
     """
-    scheme = Scheme("scheme/default.yml")
-    return scheme.construct_text(tags, True)
-
-
-def test_1_label() -> None:
-    """
-    Test tags that should be converted into single label.
-    """
-    labels = construct_labels({"name": "Name"})
-    assert len(labels) == 1
-    assert labels[0].text == "Name"
-
-
-def test_1_label_unknown_tags() -> None:
-    """
-    Test tags with some unknown tags that should be converted into single label.
-    """
-    labels = construct_labels({"name": "Name", "aaa": "bbb"})
-    assert len(labels) == 1
-    assert labels[0].text == "Name"
-
-
-def test_2_labels() -> None:
-    """
-    Test tags that should be converted into two labels.
-    """
-    labels = construct_labels({"name": "Name", "ref": "5"})
-    assert len(labels) == 2
-    assert labels[0].text == "Name"
-    assert labels[1].text == "5"
+    assert format_voltage("42") == "42 V"
+    assert format_voltage("42000") == "42 kV"