Do not skip pre-install commands when --install-only is passed (#311)

* fix: Do not skip pre-install commands when --install-only is passed

* build: Require Nox >= 2020.8.22

The `session.run_always` method is only available in 2020.8.22 and later.

Also, avoid the `^` version operator. It implies `< 2021`, preventing
installation of nox-poetry with any new Nox release.

pyproject.toml

@@ -21,7 +21,7 @@ Changelog = "https://github.com/cjolowicz/nox-poetry/releases"
 
 [tool.poetry.dependencies]
 python = "^3.6.1"
-nox = "^2020.5.24"
+nox = ">=2020.8.22"
 tomlkit = "^0.7.0"
 
 [tool.poetry.dev-dependencies]

src/nox_poetry/poetry.py

@@ -67,7 +67,7 @@ def export(self, path: Path) -> None:
         Args:
             path: The destination path.
         """
-        self.session.run(
+        self.session.run_always(
             "poetry",
             "export",
             "--format=requirements.txt",
@@ -102,7 +102,7 @@ def build(self, *, format: str) -> str:
         if not isinstance(format, DistributionFormat):
             format = DistributionFormat(format)
 
-        output = self.session.run(
+        output = self.session.run_always(
             "poetry",
             "build",
             f"--format={format}",

src/nox_poetry/sessions.py

@@ -102,7 +102,7 @@ def rewrite(arg: str, extras: Optional[str]) -> str:
 
             args = tuple(rewrite(arg, extras) for arg, extras in args_extras)
 
-            self.session.run("pip", "uninstall", "--yes", package, silent=True)
+            self.session.run_always("pip", "uninstall", "--yes", package, silent=True)
 
         requirements = self.export_requirements()
         Session_install(self.session, f"--constraint={requirements}", *args, **kwargs)
@@ -133,7 +133,7 @@ def installroot(
         package = self.build_package(distribution_format=distribution_format)
         requirements = self.export_requirements()
 
-        self.session.run("pip", "uninstall", "--yes", package, silent=True)
+        self.session.run_always("pip", "uninstall", "--yes", package, silent=True)
 
         suffix = ",".join(extras)
         if suffix.strip():

tests/unit/conftest.py

@@ -15,7 +15,7 @@ def __init__(self, path: Path) -> None:
         """Initialize."""
         self.path = path
 
-    def run(self, *args: str, **kargs: Any) -> str:
+    def run_always(self, *args: str, **kargs: Any) -> str:
         """Run."""
         path = Path("dist") / "example.whl"
         path.touch()