Set expectation when no code is used with qenv

[llrs-roche]

Pull Request

Document expectation of what should return qenv with no code.
Discovered while working on insightsengineering/teal#1630 where some code assumed it would return NULL.

Previously it was only tested that testthat::expect_identical(get_code(qenv(), names = "a"), "").
It makes sense that it also return "" when there is no code.

[github-actions]

Code Coverage Summary

Filename                         Stmts    Miss  Cover    Missing
-----------------------------  -------  ------  -------  -------------
R/qenv-c.R                          55       0  100.00%
R/qenv-class.R                      13       0  100.00%
R/qenv-concat.R                      7       0  100.00%
R/qenv-constructor.R                 1       0  100.00%
R/qenv-errors.R                      4       4  0.00%    6-9
R/qenv-eval_code.R                  60       1  98.33%   40
R/qenv-extract.R                    30       0  100.00%
R/qenv-get_code.R                   24       0  100.00%
R/qenv-get_env.R                     3       1  66.67%   27
R/qenv-get_messages.r                5       0  100.00%
R/qenv-get_outputs.R                 6       0  100.00%
R/qenv-get_var.R                    13       1  92.31%   13
R/qenv-get_warnings.R                5       0  100.00%
R/qenv-join.R                        1       1  0.00%    13
R/qenv-length.R                      2       1  50.00%   2
R/qenv-show.R                       29      29  0.00%    19-50
R/qenv-within.R                      8       0  100.00%
R/utils-get_code_dependency.R      254       3  98.82%   160, 258, 331
R/utils.R                           42       0  100.00%
TOTAL                              562      41  92.70%

Diff against main

Filename      Stmts    Miss  Cover
----------  -------  ------  --------
TOTAL             0       0  +100.00%

Results for commit: 55cd4cc

Minimum allowed coverage is 80%

♻️ This comment has been updated with latest results

[github-actions]

Unit Tests Summary

  1 files   14 suites   5s ⏱️
172 tests 169 ✅ 3 💤 0 ❌
255 runs  252 ✅ 3 💤 0 ❌

Results for commit 55cd4cc.

♻️ This comment has been updated with latest results.

[github-actions]

Unit Test Performance Difference

Additional test case details

Test Suite	$Status$	Time on main	$±Time$	Test Case
qenv_get_code	👶		$+0.01$	get_code_returns_character_of_length_0_if_no_code

Results for commit f521168

♻️ This comment has been updated with latest results.