test: update test_initial_investment_pv_and_fv

Author: chilango74

tests/portfolio/test_cashflow.py

@@ -128,10 +128,10 @@ def test_initial_investment_pv_and_fv(dcf_percentage_halfyear):
     dcf = dcf_percentage_halfyear
     dcf.discount_rate = 0.10
     dcf.mc.period = 5
+    # PV at the beginning of the historical period
     assert dcf.initial_investment_pv == dcf.wealth_index(discounting="pv", include_negative_values=False).iloc[0, 0]
-    # FV at end of forecast period
-    expected_fv = dcf.cashflow_parameters.initial_investment * (1 + dcf.discount_rate)**dcf.mc.period
-    assert dcf.initial_investment_fv == pytest.approx(expected_fv, rel=1e-12)
+    # FV at the beginning of the historical period
+    assert dcf.initial_investment_fv == dcf.wealth_index(discounting="fv", include_negative_values=False).iloc[0, 0]
 
 
 def test_wealth_index_pv_less_than_fv(dcf_indexation_yearly):