diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 2d742de..61b510a 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -36,17 +36,19 @@ jobs:
               run: |
                 python setup.py check
                 python setup.py bdist_wheel sdist
-
           - python: "3.10"
             task:
-              name: "Style"
+              name: "Lint"
               run: |
                 black --check .
           - python: "3.10"
             task:
               name: "Test"
               run: pytest --exitfirst --failed-first
-
+          - python: "3.7"
+            task:
+              name: "Test (3.7)"
+              run: pytest --exitfirst --failed-first
     steps:
       - uses: actions/checkout@v3
 
diff --git a/geoclustering/__main__.py b/geoclustering/__main__.py
index 6b2a4d0..a732727 100644
--- a/geoclustering/__main__.py
+++ b/geoclustering/__main__.py
@@ -75,14 +75,14 @@ def main(distance, size, output, filename, algorithm, _open, debug):
 
     vis = io.write_visualization(output, "result.html", encoded["geojson"])
     if vis is None:
-        print_debug(f"Skipped generating visualization: kepler is not installed.")
+        print_debug("Skipped generating visualization: kepler is not installed.")
 
     click.echo(f"Output files saved to {Path(output).absolute()}")
 
     if _open:
         if vis:
             webbrowser.open_new_tab("file://" + str(vis.absolute()))
-            print_debug(f"Opened visualization in default browser.")
+            print_debug("Opened visualization in default browser.")
         else:
             click.secho(
                 "Can't open kepler.gl: package not installed. Please re-install geoclustering with `pip install geoclustering[full]`.",
diff --git a/geoclustering/io.py b/geoclustering/io.py
index 4efe44b..55dce25 100644
--- a/geoclustering/io.py
+++ b/geoclustering/io.py
@@ -58,13 +58,16 @@ def read_csv_file(filename):
     valid_index = df.lat.apply(is_valid_lat) & df.lon.apply(is_valid_lon)
     df_invalid = df[~valid_index]
 
-    if count_invalid := len(df_invalid):
+    count_invalid = len(df_invalid)
+    if count_invalid:
         df_not_empty = df_invalid[
             (df_invalid.lat.apply(is_not_none) | df_invalid.lon.apply(is_not_none))
         ]
-        count_not_empty = len(df_not_empty)
 
-        if count_empty := count_invalid - count_not_empty:
+        count_not_empty = len(df_not_empty)
+        count_empty = count_invalid - count_not_empty
+
+        if count_empty:
             print(f"Removed {count_empty} empty coordinate pairs.")
 
         if count_not_empty:
diff --git a/tests/clustering.py b/tests/clustering.py
index 8c49874..d25fb2a 100644
--- a/tests/clustering.py
+++ b/tests/clustering.py
@@ -1,6 +1,5 @@
 from geoclustering.clustering import cluster_locations
-from geoclustering.io import read_csv_file
-from tests.helpers import get_fixture_path, read_fixture_csv
+from tests.helpers import read_fixture_csv
 
 
 df = read_fixture_csv("clustering.csv")
diff --git a/tests/encoding.py b/tests/encoding.py
index 7defb53..2be0638 100644
--- a/tests/encoding.py
+++ b/tests/encoding.py
@@ -1,4 +1,3 @@
-from geoclustering.clustering import cluster_locations
 from geoclustering.encoding import encode_clusters
 from tests.helpers import read_fixture_csv, read_fixture_content