Add some model tests (#9)

Reviewed-on: #9

test/models/expense_test.rb

@@ -1,7 +1,39 @@
 require "test_helper"
 
 class ExpenseTest < ActiveSupport::TestCase
-  # test "the truth" do
-  #   assert true
-  # end
+  def test_monthly_converts_period_for_monthly
+    expense = expenses(:monthly_expense)
+
+    assert_equal 120.00, expense.monthly
+  end
+
+  def test_monthly_converts_period_for_annually
+    expense = expenses(:annual_expense)
+
+    assert_equal 10.00, expense.monthly
+  end
+
+  def test_monthly_converts_period_for_weekly
+    expense = expenses(:weekly_expense)
+
+    assert_equal 520.00, expense.monthly
+  end
+
+  def test_monthly_converts_period_for_quarterly
+    expense = expenses(:quarterly_expense)
+
+    assert_equal 40.00, expense.monthly
+  end
+
+  def test_total_calculates_total_of_expenses
+    assert_equal 480.00, Expense.total
+  end
+
+  def test_total_calculates_monthly_total
+    assert_equal 690.00, Expense.monthly_total
+  end
+
+  def test_total_calculates_credit_card_monthly_total
+    assert_equal 130.00, Expense.credit_card_monthly_total
+  end
 end