add extra test

Author: tgolsson

src/poetry/console/commands/show.py

@@ -81,13 +81,22 @@ def handle(self) -> int | None:
         if self.option("tree"):
             self.init_styles(self.io)
 
-        if self.option("why") and self.option("tree") and package is None:
-            self.line_error(
-                "<error>Error: --why requires a package when combined with"
-                " --tree.</error>"
-            )
+        if self.option("why"):
+            if self.option("tree") and package is None:
+                self.line_error(
+                    "<error>Error: --why requires a package when combined with"
+                    " --tree.</error>"
+                )
 
-            return 1
+                return 1
+
+            if not self.option("tree") and package:
+                self.line_error(
+                    "<error>Error: --why cannot be used when displaying a single"
+                    " package.</error>"
+                )
+
+                return 1
 
         if self.option("outdated"):
             self._io.input.set_option("latest", True)

tests/console/commands/test_show.py

@@ -1680,7 +1680,9 @@ def test_show_tree_no_dev(tester: CommandTester, poetry: Poetry, installed: Repo
     assert tester.io.fetch_output() == expected
 
 
-def test_show_tree_why(tester: CommandTester, poetry: Poetry, installed: Repository):
+def test_show_tree_why_package(
+    tester: CommandTester, poetry: Poetry, installed: Repository
+):
     poetry.package.add_dependency(Factory.create_dependency("a", "=0.0.1"))
 
     a = get_package("a", "0.0.1")
@@ -1732,8 +1734,63 @@ def test_show_tree_why(tester: CommandTester, poetry: Poetry, installed: Reposit
     expected = """\
 a 0.0.1
 └── b =0.0.1
-    └── c =0.0.1
-"""
+    └── c =0.0.1 \n"""
+
+    assert tester.io.fetch_output() == expected
+
+
+def test_show_tree_why(tester: CommandTester, poetry: Poetry, installed: Repository):
+    poetry.package.add_dependency(Factory.create_dependency("a", "=0.0.1"))
+
+    a = get_package("a", "0.0.1")
+    installed.add_package(a)
+    a.add_dependency(Factory.create_dependency("b", "=0.0.1"))
+
+    b = get_package("b", "0.0.1")
+    a.add_dependency(Factory.create_dependency("c", "=0.0.1"))
+    installed.add_package(b)
+
+    c = get_package("c", "0.0.1")
+    installed.add_package(c)
+
+    poetry.locker.mock_lock_data(
+        {
+            "package": [
+                {
+                    "name": "a",
+                    "version": "0.0.1",
+                    "dependencies": {"b": "=0.0.1"},
+                    "python-versions": "*",
+                    "optional": False,
+                },
+                {
+                    "name": "b",
+                    "version": "0.0.1",
+                    "dependencies": {"c": "=0.0.1"},
+                    "python-versions": "*",
+                    "optional": False,
+                },
+                {
+                    "name": "c",
+                    "version": "0.0.1",
+                    "python-versions": "*",
+                    "optional": False,
+                },
+            ],
+            "metadata": {
+                "python-versions": "*",
+                "platform": "*",
+                "content-hash": "123456789",
+                "hashes": {"a": [], "b": [], "c": []},
+            },
+        }
+    )
+
+    tester.execute("--why")
+
+    # this has to be on a single line due to the padding whitespace, which gets stripped
+    # by pre-commit.
+    expected = """a 0.0.1        \nb 0.0.1 from a \nc 0.0.1 from b \n"""
 
     assert tester.io.fetch_output() == expected