Return figure from plot_lagged and add tests

tests/test_plot.py

@@ -0,0 +1,22 @@
+import matplotlib
+
+matplotlib.use("Agg")
+
+import os
+import sys
+import pandas as pd
+
+sys.path.append(os.path.abspath("."))
+
+from scripts.lagged_oil_unrate_chart_styled import plot_lagged
+
+
+def test_plot_lagged_returns_figure():
+    dates = pd.date_range("2000-01-01", periods=5, freq="M")
+    unrate = pd.DataFrame({"value": [5, 6, 7, 5, 4]}, index=dates)
+    oil = pd.DataFrame({"value": [20, 25, 30, 35, 40]}, index=dates)
+
+    fig = plot_lagged(unrate, oil, 1, dates[0], dates[-1], 0)
+
+    assert len(fig.axes) == 2
+    assert any(ax.get_lines() for ax in fig.axes)