diff --git a/dk-installer.py b/dk-installer.py
index 02f2ba5..cadb9ca 100755
--- a/dk-installer.py
+++ b/dk-installer.py
@@ -480,22 +480,27 @@ class Requirement:
     cmd: tuple[typing.Union[str, pathlib.Path], ...]
     fail_msg: tuple[str, ...]
     label: typing.Optional[str] = None
+    #: Second way of satisfying the same requirement, tried when ``cmd`` fails.
+    alt_cmd: typing.Optional[tuple[typing.Union[str, pathlib.Path], ...]] = None
 
     def check_availability(self, action, args, quiet=False):
-        try:
-            action.run_cmd_retries(
-                *(seg.format(**args.__dict__) for seg in self.cmd),
-                timeout=REQ_CHECK_TIMEOUT,
-                retries=1,
-            )
-        except CommandFailed:
-            if not quiet:
-                CONSOLE.space()
-                for line in self.fail_msg:
-                    CONSOLE.msg(line.format(**args.__dict__))
-            return False
-        else:
-            return True
+        for cmd in (c for c in (self.cmd, self.alt_cmd) if c is not None):
+            try:
+                action.run_cmd_retries(
+                    *(seg.format(**args.__dict__) for seg in cmd),
+                    timeout=REQ_CHECK_TIMEOUT,
+                    retries=1,
+                )
+            except CommandFailed:
+                continue
+            else:
+                return True
+
+        if not quiet:
+            CONSOLE.space()
+            for line in self.fail_msg:
+                CONSOLE.msg(line.format(**args.__dict__))
+        return False
 
 
 class CommandFailed(Exception):
@@ -1195,12 +1200,18 @@ def run(self, parent=None):
 )
 REQ_TESTGEN_IMAGE = Requirement(
     "TESTGEN_IMAGE",
-    ("docker", "manifest", "inspect", "{image}"),
+    # An image already in the local engine needs no pull, so it satisfies this outright --
+    # `docker manifest inspect` alone would reject a locally built one. Checked first because
+    # it is instant, and because it lets an install proceed from cache when the registry is
+    # unreachable. A name that is neither local nor in a registry still fails, which is the
+    # signal this requirement exists to give.
+    ("docker", "image", "inspect", "{image}"),
     (
         "The Docker engine could not access TestGen's image.",
         "Make sure your networking policy allows Docker to pull the {image} image.",
     ),
     label="TestGen image reachable",
+    alt_cmd=("docker", "manifest", "inspect", "{image}"),
 )
 
 
diff --git a/tests/test_requirement.py b/tests/test_requirement.py
new file mode 100644
index 0000000..3bb3ed4
--- /dev/null
+++ b/tests/test_requirement.py
@@ -0,0 +1,78 @@
+from argparse import Namespace
+from unittest.mock import MagicMock
+
+import pytest
+
+from tests.installer import REQ_TESTGEN_IMAGE, CommandFailed, Requirement
+
+
+def make_action(failing_cmds):
+    """An action whose run_cmd_retries fails for any command whose joined form
+    contains one of *failing_cmds*."""
+    action = MagicMock()
+
+    def run(*cmd, **kwargs):
+        joined = " ".join(str(c) for c in cmd)
+        if any(bad in joined for bad in failing_cmds):
+            raise CommandFailed()
+
+    action.run_cmd_retries.side_effect = run
+    return action
+
+
+@pytest.mark.unit
+def test_requirement_passes_on_primary_without_running_alt():
+    req = Requirement("K", ("true", "primary"), ("nope",), alt_cmd=("true", "fallback"))
+    action = make_action([])
+
+    assert req.check_availability(action, Namespace()) is True
+    # The fallback costs a round trip, so it must not run when the primary already passed.
+    assert "fallback" not in str(action.run_cmd_retries.call_args_list)
+
+
+@pytest.mark.unit
+def test_requirement_falls_through_to_alt_cmd():
+    req = Requirement("K", ("true", "primary"), ("nope",), alt_cmd=("true", "fallback"))
+
+    assert req.check_availability(make_action(["primary"]), Namespace()) is True
+
+
+@pytest.mark.unit
+def test_requirement_fails_when_neither_command_works(console_msg_mock):
+    req = Requirement("K", ("true", "primary"), ("it broke",), alt_cmd=("true", "fallback"))
+
+    assert req.check_availability(make_action(["primary", "fallback"]), Namespace()) is False
+    console_msg_mock.assert_any_msg_contains("it broke")
+
+
+@pytest.mark.unit
+def test_requirement_without_alt_cmd_still_fails_cleanly(console_msg_mock):
+    """The alt_cmd default must not change how single-command requirements behave."""
+    req = Requirement("K", ("true", "primary"), ("it broke",))
+
+    assert req.check_availability(make_action(["primary"]), Namespace()) is False
+    console_msg_mock.assert_any_msg_contains("it broke")
+
+
+@pytest.mark.unit
+@pytest.mark.parametrize(
+    "available, expected",
+    (
+        ("local", True),  # built locally, absent from any registry
+        ("registry", True),  # normal install: pullable, not yet local
+        ("neither", False),  # a typo'd name or an unreachable registry
+    ),
+)
+def test_testgen_image_accepts_local_or_registry(available, expected):
+    """A locally built image needs no pull, so it satisfies the check. A name that is
+    neither local nor pullable still fails -- that is the signal the check exists for."""
+    failing = {
+        "local": ["manifest inspect"],
+        "registry": ["image inspect"],
+        "neither": ["manifest inspect", "image inspect"],
+    }[available]
+
+    action = make_action(failing)
+    args = Namespace(image="dataops-testgen-local:dev")
+
+    assert REQ_TESTGEN_IMAGE.check_availability(action, args, quiet=True) is expected