Add unit test for get_pretty_snapshot_diff(...).

tests/backend/model_management/test_memory_snapshot.py

@@ -0,0 +1,35 @@
+import pytest
+
+from invokeai.backend.model_management.libc_util import Struct_mallinfo2
+from invokeai.backend.model_management.memory_snapshot import MemorySnapshot, get_pretty_snapshot_diff
+
+
+def test_memory_snapshot_capture():
+    """Smoke test of MemorySnapshot.capture()."""
+    snapshot = MemorySnapshot.capture()
+
+    # We just check process_ram, because it is the only field that should be supported on all platforms.
+    assert snapshot.process_ram > 0
+
+
+snapshots = [
+    MemorySnapshot(process_ram=1.0, vram=2.0, malloc_info=Struct_mallinfo2()),
+    MemorySnapshot(process_ram=1.0, vram=2.0, malloc_info=None),
+    MemorySnapshot(process_ram=1.0, vram=None, malloc_info=Struct_mallinfo2()),
+    MemorySnapshot(process_ram=1.0, vram=None, malloc_info=None),
+]
+
+
+@pytest.mark.parametrize("snapshot_1", snapshots)
+@pytest.mark.parametrize("snapshot_2", snapshots)
+def test_get_pretty_snapshot_diff(snapshot_1, snapshot_2):
+    """Test that get_pretty_snapshot_diff() works with various combinations of missing MemorySnapshot fields."""
+    msg = get_pretty_snapshot_diff(snapshot_1, snapshot_2)
+
+    expected_lines = 1
+    if snapshot_1.vram is not None and snapshot_2.vram is not None:
+        expected_lines += 1
+    if snapshot_1.malloc_info is not None and snapshot_2.malloc_info is not None:
+        expected_lines += 5
+
+    assert len(msg.splitlines()) == expected_lines