[uptime] Skip the timestamp sensor source unless a timestamp sensor is configured (#18746)

tests/component_tests/uptime/config/seconds.yaml

@@ -0,0 +1,20 @@
+esphome:
+  name: test
+
+esp32:
+  board: esp32dev
+  framework:
+    type: esp-idf
+
+wifi:
+  ssid: "test_ssid"
+  password: "test_password"
+
+time:
+  - platform: sntp
+    id: sntp_time
+
+sensor:
+  - platform: uptime
+    name: Uptime Seconds
+    type: seconds

tests/component_tests/uptime/config/timestamp.yaml

@@ -0,0 +1,20 @@
+esphome:
+  name: test
+
+esp32:
+  board: esp32dev
+  framework:
+    type: esp-idf
+
+wifi:
+  ssid: "test_ssid"
+  password: "test_password"
+
+time:
+  - platform: sntp
+    id: sntp_time
+
+sensor:
+  - platform: uptime
+    name: Uptime Timestamp
+    type: timestamp

tests/component_tests/uptime/test_uptime.py

@@ -0,0 +1,27 @@
+"""The timestamp uptime sensor source is only compiled when that type is used,
+so the define must follow the configured sensor type rather than time: alone."""
+
+from collections.abc import Callable
+from pathlib import Path
+
+import pytest
+
+from esphome.core import CORE
+
+
+@pytest.mark.parametrize(
+    ("fixture", "emits"),
+    [
+        ("seconds.yaml", False),
+        ("timestamp.yaml", True),
+    ],
+)
+def test_timestamp_define_follows_sensor_type(
+    fixture: str,
+    emits: bool,
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    generate_main(component_config_path(fixture))
+    defines = {define.name for define in CORE.defines}
+    assert ("USE_UPTIME_TIMESTAMP" in defines) is emits