test(growth): add bmi test

test/growth/calc/bmi_test.exs

@@ -0,0 +1,23 @@
+defmodule Growth.Calc.BMITest do
+  @moduledoc false
+
+  use ExUnit.Case, async: true
+
+  alias Growth.Calc.BMI
+
+  describe "calculate/3" do
+    test "in metric system" do
+      weight_kg = 78.5
+      height_cm = 168.2
+
+      assert 27.74710475751505 == BMI.calculate(:metric, weight_kg, height_cm)
+    end
+
+    test "in english system" do
+      weight_lb = 173.1
+      height_in = 66.2
+
+      assert 27.770202207557876 == BMI.calculate(:english, weight_lb, height_in)
+    end
+  end
+end