Extract the shared native-build helpers from the ESP-IDF backend

tests/unit_tests/test_size_summary.py

@@ -126,3 +126,33 @@ def test_print_summary_handles_no_memory_types(
     size_json = _write_size_json(tmp_path, {"image_size": 0})
     print_summary(size_json, partitions_csv=None)
     assert capsys.readouterr().out == ""
+
+
+def test_format_bar_zero_total() -> None:
+    """A zero total must not divide by zero."""
+    from esphome.espidf.size_summary import format_bar
+
+    assert format_bar(0, 0) == "[          ]   0.0% (used 0 bytes from 0 bytes)"
+
+
+def test_print_summary_flash_line(
+    tmp_path: Path, capsys: pytest.CaptureFixture[str]
+) -> None:
+    """image_size + a factory app partition produce the Flash line."""
+    size_json = tmp_path / "esp_idf_size.json"
+    size_json.write_text(
+        json.dumps(
+            {
+                "memory_types": {"DRAM": {"used": 100, "size": 200}},
+                "image_size": 500,
+            }
+        )
+    )
+    partitions = tmp_path / "partitions.csv"
+    partitions.write_text(
+        "# name, type, subtype, offset, size\napp0, app, factory, 0x10000, 0x100000\n"
+    )
+    print_summary(size_json, partitions)
+    out = capsys.readouterr().out
+    assert "RAM:   [=====     ]  50.0% (used 100 bytes from 200 bytes)" in out
+    assert "Flash: [          ]   0.0% (used 500 bytes from 1048576 bytes)" in out