R client: remove call to "Observe" in the C++ client, add missing dep…

…endencies (deephaven#4600)

* R Client: remove call to Observe, add dependencies to README

* move test package install to a different part of the README

R/rdeephaven/README.md

@@ -161,7 +161,12 @@ this means that the C++ compiler does not know where to find the relevant header
 
 ## Running the unit tests
 
-The Deephaven R client utilizes R's `testthat` package to perform unit tests. In order to run these unit tests, install `testthat` via `install.packages("testthat")`. Then, from an R session with `rdeephaven` installed, run the unit tests:
+The Deephaven R client utilizes R's `testthat` package to perform unit tests. In order to run these unit tests, install `testthat` and the other dependent packages:
+```r
+install.packages(c('testthat', 'lubridate', 'zoo'))
+```
+
+Then, from an R session with `rdeephaven` installed, run the unit tests:
 ```r
 library(testthat)
 test_package("rdeephaven")

R/rdeephaven/src/client.cpp

@@ -673,10 +673,9 @@ class ClientWrapper {
      * @return Boolean indicating whether table_name exists on the server or not.
     */
     bool CheckForTable(std::string table_name) {
-        // we have to first fetchTable to check existence, fetchTable does not fail on its own, but .observe() will fail if table doesn't exist
-        deephaven::client::TableHandle table_handle = internal_tbl_hdl_mngr.FetchTable(table_name);
+        // we have to fetchTable to check existence.
         try {
-            table_handle.Observe();
+            deephaven::client::TableHandle table_handle = internal_tbl_hdl_mngr.FetchTable(table_name);
         } catch(...) {
             return false;
         }