Add a test of pure lock deletes for complex deps. (#2576)

I claimed there was already one of these in #2569 but I was wrong
because the existing complex case test include an update; so is not a
pure delete.

Add a new test of the pure delete case where the deleted node's graph
is partially retained.

tests/integration/cli/commands/test_lock_update_issues_2332_2334.py

@@ -80,13 +80,13 @@ def populate_find_links_repo_initial(
     # N.B.: Since we are setting up a find links repo for offline lock resolves, we grab one
     # distribution online to allow the current Pip version to bootstrap itself if needed.
     result = resolver.resolve_requirements(
-        ["ansicolors==1.1.8"], result_type=InstallableType.WHEEL_FILE
+        ["ansicolors==1.1.8", "cowsay==6.0.0"], result_type=InstallableType.WHEEL_FILE
     )
     for resolved_distribution in result.distributions:
         find_links_repo.host(resolved_distribution.distribution.location)
 
     find_links_repo.make_wheel("proj-c", "1")
-    find_links_repo.make_wheel("proj-b", "1", requirements=["proj-a", "proj-c"])
+    find_links_repo.make_wheel("proj-b", "1", requirements=["proj-a", "proj-c", "cowsay"])
     find_links_repo.make_wheel("proj-a", "1", requirements=["proj-c", "ansicolors"])
     find_links_repo.make_wheel("proj-a", "1.1", requirements=["proj-c", "ansicolors"])
 
@@ -277,6 +277,7 @@ def test_lock_update_conflict(
 
                     The following lock update constraints could not all be satisfied:
                     ansicolors==1.1.8
+                    cowsay==6
                     proj-a==1.1
                     proj-b>=2
                     proj-c==1
@@ -377,6 +378,7 @@ def test_lock_update_delete_nominal(
             dedent(
                 """\
                 Updates for lock generated by universal:
+                  Deleted cowsay 6
                   Deleted proj-b 1
                 Updates to lock input requirements:
                   Deleted 'proj-b==1.*'
@@ -450,6 +452,7 @@ def test_lock_update_mixed(
             dedent(
                 """\
                 Updates for lock generated by universal:
+                  Deleted cowsay 6
                   Deleted proj-b 1
                   Deleted proj-c 1
                   Updated proj-a from 1.1 to 2
@@ -462,3 +465,32 @@ def test_lock_update_mixed(
     lockfile = json_codec.load(lock, path_mappings)
     locked_requirements = locked_requirement_pins(lockfile)
     assert {pin("proj-a", "2"), pin("ansicolors", "1.1.8")} == locked_requirements
+
+
+def test_lock_delete_complex(
+    run_lock_update,  # type: RunLockUpdate
+    lock,  # type: str
+    path_mappings,  # type: PathMappings
+):
+    # type: (...) -> None
+
+    run_lock_update("-d", "proj-b").assert_success(
+        expected_error_re=re_exact(
+            dedent(
+                """\
+                Updates for lock generated by universal:
+                  Deleted cowsay 6
+                  Deleted proj-b 1
+                Updates to lock input requirements:
+                  Deleted 'proj-b==1.*'
+                """
+            )
+        )
+    )
+    lockfile = json_codec.load(lock, path_mappings)
+    locked_requirements = locked_requirement_pins(lockfile)
+    assert {
+        pin("proj-a", "1.1"),
+        pin("proj-c", "1"),
+        pin("ansicolors", "1.1.8"),
+    } == locked_requirements