Executor: Remove duplicate entry with dry-run argument (#4660)

# Pull Request Check List

Resolves: #3097 

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- [x] Added **tests** for changed code. I adapted the test in the `tests/console/commands/plugin/test_remove.py` file to reflect the bug fix.
- [ ] Updated **documentation** for changed code.

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Apart from running the ci linting steps and pytest locally for both python 3.6 and 3.8, I also tested the code by running
```
docker run --rm -i --entrypoint bash python:3.8 <<EOF
set -e
python -m pip install -q git+https://github.com/mmacchia/poetry.git@issue/3097
python -m poetry new foobar
pushd foobar
sed -i /pytest/d pyproject.toml
python -m poetry add --dry-run pycowsay
python -m poetry run pip list
EOF
```
The corresponding output is:
```
Created package foobar in foobar
/foobar /
Creating virtualenv foobar-lWDpn5M1-py3.8 in /root/.cache/pypoetry/virtualenvs
Using version ^0.0.0.1 for pycowsay

Updating dependencies
Resolving dependencies...

Writing lock file

Package operations: 1 install, 0 updates, 0 removals

  • Installing pycowsay (0.0.0.1)
Package    Version
---------- -------
pip        21.2.4
setuptools 58.1.0
wheel      0.37.0
```
As expected, the command `poetry add --dry-run pycowsay` yielded a single output (` • Installing pycowsay (0.0.0.1)`) and did not add the package to the project (see the output of `poetry run pip list`).

The change in the PR solves the duplication issue because the creation of the console output when `not self._enabled` is taken care of by the boolean output of the`self._should_write_operation(operation)` function.

Please feel free to get in touch if I can help adding more test cases for the `--dry-run` argument or the `_enabled` flag and to add any feedback. I would be happy to improve/clarify the code in this PR.

Co-authored-by: Marco Macchia <mmacchia@wayfair.com>

src/poetry/installation/executor.py

@@ -316,8 +316,6 @@ class Executor:
             return 0
             return 0
 
 
         if not self._enabled or self._dry_run:
         if not self._enabled or self._dry_run:
-            self._io.write_line(f"  <fg=blue;options=bold>•</> {operation_message}")
-
             return 0
             return 0
 
 
         result: int = getattr(self, f"_execute_{method}")(operation)
         result: int = getattr(self, f"_execute_{method}")(operation)
@@ -723,7 +721,9 @@ class Executor:
         return archive
         return archive
 
 
     def _should_write_operation(self, operation: Operation) -> bool:
     def _should_write_operation(self, operation: Operation) -> bool:
-        return not operation.skipped or self._dry_run or self._verbose
+        return (
+            not operation.skipped or self._dry_run or self._verbose or not self._enabled
+        )
 
 
     def _save_url_reference(self, operation: Operation) -> None:
     def _save_url_reference(self, operation: Operation) -> None:
         """
         """

tests/console/commands/self/test_remove_plugins.py

@@ -96,7 +96,6 @@ Resolving dependencies...
 Package operations: 0 installs, 0 updates, 1 removal, 1 skipped
 Package operations: 0 installs, 0 updates, 1 removal, 1 skipped
 
 
   • Removing poetry-plugin (1.2.3)
   • Removing poetry-plugin (1.2.3)
-  • Removing poetry-plugin (1.2.3)
   • Installing poetry ({__version__}): Skipped for the following reason: Already \
   • Installing poetry ({__version__}): Skipped for the following reason: Already \
 installed
 installed
 """
 """