test: 🧪❌ Create specification for the registry – interface for persis…

…tent storage

- Add unit tests for an object that the app will interact with to store data to a persistent storage.
- I want to use a `registry` object to run operations on a `storage` object. The storage will be a CSV file, but it could as well be a database connection or a S3 bucket.
- This is an implementation detail of the app, it doesn't change the behavior of the app – tests are added to `tests/testthat/`, no changes in acceptance tests are needed.

tests/testthat/test-registry.R

@@ -0,0 +1,155 @@
+box::use(
+  glue[glue],
+  testthat[...], # nolint
+  withr[with_tempdir],
+)
+
+box::use(
+  app / registry,
+  app / transaction,
+)
+
+# Fake storage
+create_storage <- function() {
+  .storage <- glue::glue("store_session_{as.numeric(Sys.time())}.csv")
+  write.csv(data.frame(amount = numeric()), .storage, row.names = FALSE)
+  .storage
+}
+
+describe("record", {
+  it("should record a transaction", {
+    with_tempdir({
+      # Arrange
+      .storage <- create_storage()
+      .registry <- registry$new(.storage)
+
+      # Act
+      .registry$record(transaction$new(100)) # nolint
+
+      # Assert
+      expect_equal(nrow(read.csv(.storage)), 1)
+    })
+  })
+
+  it("should record multiple transactions", {
+    with_tempdir({
+      # Arrange
+      .storage <- create_storage()
+      .registry <- registry$new(.storage)
+
+      # Act
+      .registry$record(transaction$new(100)) # nolint
+      .registry$record(transaction$new(100)) # nolint
+
+      # Assert
+      expect_equal(nrow(read.csv(.storage)), 2)
+    })
+  })
+
+  it("should throw an error if storage doesn't exist", {
+    # Arrange
+    with_tempdir({
+      .storage <- create_storage()
+    })
+
+    # Act, Assert
+    expect_error(
+      registry$new(.storage),
+      regexp = glue("File {.storage} does not exist"),
+      fixed = TRUE
+    )
+  })
+})
+
+describe("get_total_positive", {
+  it("should return the total of positive transactions", {
+    with_tempdir({
+      # Arrange
+      .storage <- create_storage()
+      .registry <- registry$new(.storage)
+
+      # Act
+      .registry$record(transaction$new(100)) # nolint
+      .registry$record(transaction$new(-100)) # nolint
+
+      # Assert
+      expect_equal(.registry$get_total_positive(), 100)
+    })
+  })
+
+  it("should return 0 if there are no transactions", {
+    with_tempdir({
+      # Arrange
+      .storage <- create_storage()
+      .registry <- registry$new(.storage)
+
+      # Act
+      result <- .registry$get_total_positive()
+
+      # Assert
+      expect_equal(result, 0)
+    })
+  })
+})
+
+describe("get_total_negative", {
+  it("should return the total of negative transactions", {
+    with_tempdir({
+      # Arrange
+      .storage <- create_storage()
+      .registry <- registry$new(.storage)
+
+      # Act
+      .registry$record(transaction$new(200)) # nolint
+      .registry$record(transaction$new(-100)) # nolint
+
+      # Assert
+      expect_equal(.registry$get_total_negative(), 100)
+    })
+  })
+
+  it("should return 0 if there are no transactions", {
+    with_tempdir({
+      # Arrange
+      .storage <- create_storage()
+      .registry <- registry$new(.storage)
+
+      # Act
+      result <- .registry$get_total_negative()
+
+      # Assert
+      expect_equal(result, 0)
+    })
+  })
+})
+
+describe("get_total", {
+  it("should return the total of all transactions", {
+    with_tempdir({
+      # Arrange
+      .storage <- create_storage()
+      .registry <- registry$new(.storage)
+
+      # Act
+      .registry$record(transaction$new(100)) # nolint
+      .registry$record(transaction$new(-100)) # nolint
+
+      # Assert
+      expect_equal(.registry$get_total(), 0)
+    })
+  })
+
+  it("should return 0 if there are no transactions", {
+    with_tempdir({
+      # Arrange
+      .storage <- create_storage()
+      .registry <- registry$new(.storage)
+
+      # Act
+      result <- .registry$get_total()
+
+      # Assert
+      expect_equal(result, 0)
+    })
+  })
+})