diff --git a/test/test_color.py b/test/test_color.py
index a60366c..2a103a6 100644
--- a/test/test_color.py
+++ b/test/test_color.py
@@ -1,12 +1,15 @@
+"""
+Test color functions.
+"""
 from colour import Color
 
 from roentgen.color import is_bright
 
-__author__: str = "Sergey Vartanov"
-__email__: str = "me@enzet.ru"
+__author__ = "Sergey Vartanov"
+__email__ = "me@enzet.ru"
 
 
-def test_is_bright():
+def test_is_bright() -> None:
     """
     Test detecting color brightness.
     """
diff --git a/test/test_flinger.py b/test/test_flinger.py
new file mode 100644
index 0000000..f02c1d5
--- /dev/null
+++ b/test/test_flinger.py
@@ -0,0 +1,32 @@
+"""
+Test coordinates computation.
+"""
+import numpy as np
+
+from roentgen.flinger import (
+    pseudo_mercator,
+    osm_zoom_level_to_pixels_per_meter,
+)
+
+__author__ = "Sergey Vartanov"
+__email__ = "me@enzet.ru"
+
+
+def test_pseudo_mercator() -> None:
+    """
+    Test pseudo-Mercator projection.
+    """
+    assert np.allclose(pseudo_mercator(np.array((0, 0))), np.array((0, 0)))
+    assert np.allclose(pseudo_mercator(np.array((0, 10))), np.array((10, 0)))
+    assert np.allclose(
+        pseudo_mercator(np.array((10, 0))), np.array((0, 10.05115966))
+    )
+
+
+def test_osm_zoom_level_to_pixels_per_meter() -> None:
+    """
+    Test scale computation.
+    """
+    assert np.allclose(
+        osm_zoom_level_to_pixels_per_meter(18), 1.6759517949045808
+    )
diff --git a/test/test_icons.py b/test/test_icons.py
index 5278930..8b8e203 100644
--- a/test/test_icons.py
+++ b/test/test_icons.py
@@ -4,6 +4,7 @@ Test icon generation for nodes.
 from os import makedirs
 from typing import Dict
 
+from roentgen.icon import IconSet
 from roentgen.grid import draw_all_icons
 from test import SCHEME, SCHEME_EXTRACTOR
 
@@ -12,12 +13,17 @@ __email__ = "me@enzet.ru"
 
 
 def test_icons() -> None:
-    """ Test grid drawing. """
+    """
+    Test grid drawing.
+    """
     makedirs("icon_set", exist_ok=True)
     draw_all_icons(SCHEME, SCHEME_EXTRACTOR, "temp.svg", "icon_set")
 
 
-def get_icon(tags: Dict[str, str]):
+def get_icon(tags: Dict[str, str]) -> IconSet:
+    """
+    Construct icon from tags.
+    """
     icon, _ = SCHEME.get_icon(SCHEME_EXTRACTOR, tags)
     return icon
 
diff --git a/test/test_osm_reader.py b/test/test_osm_reader.py
index dec5694..fa8a681 100644
--- a/test/test_osm_reader.py
+++ b/test/test_osm_reader.py
@@ -4,6 +4,9 @@ Test OSM XML parsing.
 import numpy as np
 from roentgen.osm_reader import OSMNode, OSMReader, OSMRelation, OSMWay
 
+__author__ = "Sergey Vartanov"
+__email__ = "me@enzet.ru"
+
 
 def test_node() -> None:
     """