Fixes datanames() assignment and re-adds test for deprecated functi…

…on (#350)

# Pull Request

Part of #333 

#### Changes description

- Method was incorrectly overwriting the `teal_data` object with their
own names
- Adds test that will continue to test the functionality until it's
removed from the framework

Co-authored-by: Marcin <[email protected]>

R/deprecated.R

@@ -377,7 +377,7 @@ datanames <- function(x) {
     "`datanames<-`()",
     details = "invalid to use `datanames()<-` or `names()<-` on an object of class `teal_data`. See ?names.teal_data"
   )
-  names(x)
+  x
 }
 
 #' @rdname datanames

tests/testthat/test-deprecated.R

@@ -0,0 +1,34 @@
+testthat::describe("datanames deprecation: ", {
+  testthat::it("setter does nothing to object", {
+    td <- teal_data() |>
+      within({
+        iris <- iris
+        mtcars <- mtcars
+      })
+
+    # ignore deprecation warnings
+    withr::local_options(lifecycle_verbosity = "quiet")
+    datanames(td) <- c("mtcars")
+
+    testthat::expect_equal(
+      td,
+      teal_data() |>
+        within({
+          iris <- iris
+          mtcars <- mtcars
+        })
+    )
+  })
+
+  testthat::it("getter returns same as `names()`", {
+    td <- teal_data() |>
+      within({
+        iris <- iris
+        mtcars <- mtcars
+      })
+
+    # ignore deprecation warnings
+    withr::local_options(lifecycle_verbosity = "quiet")
+    testthat::expect_setequal(datanames(td), names(td))
+  })
+})