test: 🧪❌ Add specification for CSV storage

- Create a specification for an interface that will connect the app with a CSV file.

tests/testthat/test-storage.R

@@ -0,0 +1,24 @@
+box::use(
+  fs[file_exists],
+  testthat[...], # nolint
+  withr[with_tempdir],
+)
+
+box::use(
+  app / storage,
+)
+
+describe("new", {
+  it("should create a new csv storage if csv path is provided", {
+    with_tempdir({
+      # Arrange
+      path <- "store.csv"
+
+      # Act
+      .storage <- storage$new(path, schema = list(amount = numeric()))
+
+      # Assert
+      expect_true(file_exists(.storage))
+    })
+  })
+})