feat: 实现指标详情子页（周/月切换 + 趋势图）

替换 MetricDetailPlaceholder 为真实详情页：范围切换、柱状趋势图、平均/最高/最低摘要，
睡眠指标额外渲染深睡/浅睡/清醒分期条与入睡/起床时间。
新增 MetricDetailViewModel（flatMapLatest 重新订阅数据源）与其 3 条 JVM 测试、
RoutesTest（锁住路由模板与 Routes.detail() 拼串）、Formatters.formatDecimal 与其测试。
接入 RingHealthApp 的 DETAIL_PATTERN，参数无法解析时直接抛而不是静默兜底。

Co-Authored-By: Claude Code <noreply@anthropic.com>

app/src/main/java/com/placeholder/ringhealth/core/common/Formatters.kt

@@ -45,6 +45,9 @@ fun formatClock(timestamp: Long): String =
 fun formatDate(timestamp: Long): String =
     SimpleDateFormat("yyyy-MM-dd", Locale.CHINA).format(Date(timestamp))
 
+/** 数值 → 保留一位小数。详情页的统计摘要用（ledger Ruling R29）。 */
+fun formatDecimal(value: Double): String = String.format(Locale.CHINA, "%.1f", value)
+
 /** 压力值 → 字符串资源 id。中文描述的唯一来源是 `strings.xml`（ledger Ruling R13）。 */
 @StringRes
 fun stressLevelLabelRes(stress: Int): Int = when {

app/src/main/java/com/placeholder/ringhealth/core/navigation/RingHealthApp.kt

@@ -29,7 +29,7 @@ import com.placeholder.ringhealth.R
 import com.placeholder.ringhealth.domain.model.MetricType
 import com.placeholder.ringhealth.feature.device.DeviceScreen
 import com.placeholder.ringhealth.feature.device.DeviceSettingsScreen
-import com.placeholder.ringhealth.feature.detail.MetricDetailPlaceholder
+import com.placeholder.ringhealth.feature.detail.MetricDetailScreen
 import com.placeholder.ringhealth.feature.home.HomeScreen
 import com.placeholder.ringhealth.feature.profile.ProfileScreen
 import com.placeholder.ringhealth.feature.workout.WorkoutHistoryScreen
@@ -114,9 +114,16 @@ fun RingHealthApp(navController: NavHostController = rememberNavController()) {
                 route = Routes.DETAIL_PATTERN,
                 arguments = listOf(navArgument(Routes.DETAIL_ARG_METRIC) { type = NavType.StringType }),
             ) { entry ->
-                val raw = entry.arguments?.getString(Routes.DETAIL_ARG_METRIC).orEmpty()
-                val metric = MetricType.entries.firstOrNull { it.name == raw } ?: MetricType.STEP
-                MetricDetailPlaceholder(metric = metric)
+                // 参数无法解析属于编程错误，直接抛（ledger Ruling R22）：这里原先是
+                // `?: MetricType.STEP`，一旦路由模板与 Routes.detail() 拼串不一致，
+                // 页面会静默显示步数的数据而不报错 —— 那是「错数据」而不是「响亮失败」。
+                val raw = requireNotNull(entry.arguments?.getString(Routes.DETAIL_ARG_METRIC)) {
+                    "详情路由缺少参数 ${Routes.DETAIL_ARG_METRIC}"
+                }
+                val metric = requireNotNull(MetricType.entries.firstOrNull { it.name == raw }) {
+                    "无法识别的指标：$raw"
+                }
+                MetricDetailScreen(metric = metric, onBack = { navController.popBackStack() })
             }
         }
     }

app/src/main/java/com/placeholder/ringhealth/feature/detail/MetricDetailScreen.kt

@@ -1,19 +1,322 @@
 package com.placeholder.ringhealth.feature.detail
 
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
+import androidx.compose.material3.CircularProgressIndicator
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.FilterChip
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Text
+import androidx.compose.material3.TopAppBar
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.tooling.preview.Preview
+import androidx.compose.ui.unit.dp
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import androidx.lifecycle.viewmodel.compose.viewModel
 import com.placeholder.ringhealth.R
+import com.placeholder.ringhealth.core.common.formatClock
+import com.placeholder.ringhealth.core.common.formatDecimal
+import com.placeholder.ringhealth.core.designsystem.MetricBlue
+import com.placeholder.ringhealth.core.designsystem.MetricGreen
+import com.placeholder.ringhealth.core.designsystem.RingHealthTheme
+import com.placeholder.ringhealth.core.designsystem.TextSecondary
+import com.placeholder.ringhealth.core.designsystem.component.HealthCard
+import com.placeholder.ringhealth.core.designsystem.component.MetricBarChart
+import com.placeholder.ringhealth.core.designsystem.component.SectionHeader
+import com.placeholder.ringhealth.core.designsystem.component.StatBar
+import com.placeholder.ringhealth.core.designsystem.component.StatSegment
+import com.placeholder.ringhealth.domain.model.DateRange
+import com.placeholder.ringhealth.domain.model.MetricPoint
 import com.placeholder.ringhealth.domain.model.MetricType
 
-/** 指标详情子页（占位，待 Task 12 实现）。 */
+/**
+ * 指标详情页（有状态外壳）。
+ *
+ * 本页自带 `Scaffold` + `TopAppBar`（外层 `RingHealthApp` 也有一个 `Scaffold`，
+ * 它传入的 `innerPadding` 已用于 NavHost 的 `Modifier.padding`，底部栏因此保持可见）。
+ * 页面内容全部在 `MetricDetailContent` 里，本函数只负责取状态与传回调（ledger Ruling R26）。
+ */
 @Composable
-fun MetricDetailPlaceholder(metric: MetricType, modifier: Modifier = Modifier) {
-    Box(modifier = modifier.fillMaxSize(), contentAlignment = Alignment.Center) {
-        Text(stringResource(R.string.placeholder_metric_detail))
+fun MetricDetailScreen(
+    metric: MetricType,
+    onBack: () -> Unit,
+    modifier: Modifier = Modifier,
+    viewModel: MetricDetailViewModel = viewModel(factory = MetricDetailViewModel.factory(metric)),
+) {
+    val state by viewModel.uiState.collectAsStateWithLifecycle()
+    MetricDetailContent(
+        state = state,
+        onBack = onBack,
+        onSelectRange = viewModel::switchRange,
+        modifier = modifier,
+    )
+}
+
+/**
+ * 无状态指标详情内容：范围切换 + 柱状趋势图 + 统计摘要（+ 睡眠分期）。
+ *
+ * 标题取自 `state.metric` 而不是外面传进来的 `metric` —— 无状态层只有 `state` 一个数据来源，
+ * 免得出现「标题写心率、数据画睡眠」这种两者不一致的可能。
+ */
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+private fun MetricDetailContent(
+    state: MetricDetailUiState,
+    onBack: () -> Unit,
+    onSelectRange: (DateRange) -> Unit,
+    modifier: Modifier = Modifier,
+) {
+    Scaffold(
+        modifier = modifier,
+        containerColor = MaterialTheme.colorScheme.background,
+        topBar = {
+            TopAppBar(
+                title = { Text(text = stringResource(metricTitleRes(state.metric))) },
+                navigationIcon = {
+                    IconButton(onClick = onBack) {
+                        Icon(
+                            imageVector = Icons.AutoMirrored.Filled.ArrowBack,
+                            contentDescription = stringResource(R.string.action_back),
+                        )
+                    }
+                },
+            )
+        },
+    ) { innerPadding ->
+        if (state.loading) {
+            Box(
+                modifier = Modifier.fillMaxSize().padding(innerPadding),
+                contentAlignment = Alignment.Center,
+            ) {
+                CircularProgressIndicator(color = MetricGreen)
+            }
+            return@Scaffold
+        }
+
+        LazyColumn(
+            modifier = Modifier.fillMaxSize().padding(innerPadding),
+            contentPadding = PaddingValues(16.dp),
+            verticalArrangement = Arrangement.spacedBy(12.dp),
+        ) {
+            item { RangeSelector(current = state.range, onSelect = onSelectRange) }
+            item {
+                HealthCard {
+                    SectionHeader(title = stringResource(R.string.detail_trend))
+                    MetricBarChart(
+                        values = state.points.map { it.value.toFloat() },
+                        color = MetricGreen,
+                    )
+                }
+            }
+            item {
+                HealthCard {
+                    val values = state.points.map { it.value }
+                    StatLine(label = stringResource(R.string.detail_average), value = values.averageOrZero())
+                    StatLine(label = stringResource(R.string.detail_max), value = values.maxOrNull() ?: 0.0)
+                    StatLine(label = stringResource(R.string.detail_min), value = values.minOrNull() ?: 0.0)
+                }
+            }
+            if (state.metric == MetricType.SLEEP) {
+                item { SleepStagesCard(points = state.points) }
+            }
+        }
+    }
+}
+
+/**
+ * 睡眠分期卡片：深睡/浅睡/清醒分段条 + 入睡/起床时间（对应 spec §6 的 `detail/sleep`）。
+ */
+@Composable
+private fun SleepStagesCard(points: List<MetricPoint>, modifier: Modifier = Modifier) {
+    // 阶段一没有真实分期数据，按固定比例演示；M3 接入真实睡眠数据后改为按实际时段计算。
+    val segments = listOf(
+        StatSegment(weight = 0.25f, color = MetricBlue),
+        StatSegment(weight = 0.65f, color = MetricBlue.copy(alpha = 0.45f)),
+        StatSegment(weight = 0.10f, color = MetricBlue.copy(alpha = 0.2f)),
+    )
+    HealthCard(modifier = modifier) {
+        SectionHeader(title = stringResource(R.string.detail_sleep_stages))
+        StatBar(segments = segments)
+        Row(
+            modifier = Modifier.fillMaxWidth().padding(top = 12.dp),
+            horizontalArrangement = Arrangement.SpaceBetween,
+        ) {
+            StageLegend(label = stringResource(R.string.detail_sleep_deep), tint = MetricBlue)
+            StageLegend(label = stringResource(R.string.detail_sleep_light), tint = MetricBlue.copy(alpha = 0.45f))
+            StageLegend(label = stringResource(R.string.detail_sleep_awake), tint = MetricBlue.copy(alpha = 0.2f))
+        }
+        // 入睡/起床演示值（ledger Ruling R29）：Mock 的睡眠历史点是「每天一个」，首点是 7 天前、
+        // 末点是现在。直接拿 first/last 当入睡/起床会显示成「睡了 7 天」，在验收时看着像 bug。
+        // 这里改成以最后一个数据点为起床时刻、往前推 8 小时作为入睡时刻 —— 一张卡片讲「一晚」。
+        // M3 接入真实睡眠数据后改为读取实际分期时段。
+        val wakeUp = points.lastOrNull()?.timestamp
+        if (wakeUp != null) {
+            // 只有拿到起床时刻才渲染这一行；入睡时刻由它推出，所以判空只需判 wakeUp
+            // （brief 原文写的是 `fallAsleep != null && wakeUp != null`，Kotlin 会因其恒真而告警，
+            // 语义与此处完全等价）。
+            val fallAsleep = wakeUp - DEMO_SLEEP_WINDOW_MILLIS
+            Row(
+                modifier = Modifier.fillMaxWidth().padding(top = 12.dp),
+                horizontalArrangement = Arrangement.SpaceBetween,
+            ) {
+                Text(
+                    text = "${stringResource(R.string.detail_sleep_fall_asleep)} ${formatClock(fallAsleep)}",
+                    style = MaterialTheme.typography.bodySmall,
+                    color = TextSecondary,
+                )
+                Text(
+                    text = "${stringResource(R.string.detail_sleep_wake_up)} ${formatClock(wakeUp)}",
+                    style = MaterialTheme.typography.bodySmall,
+                    color = TextSecondary,
+                )
+            }
+        }
+    }
+}
+
+/** 阶段一演示用的「一晚」时长：8 小时。M3 接入真实睡眠数据后删除。 */
+private const val DEMO_SLEEP_WINDOW_MILLIS = 8L * 60 * 60 * 1000
+
+/** 分期图例：小色块 + 名称。 */
+@Composable
+private fun StageLegend(label: String, tint: Color, modifier: Modifier = Modifier) {
+    Row(modifier = modifier, verticalAlignment = Alignment.CenterVertically) {
+        Box(
+            modifier = Modifier
+                .size(10.dp)
+                .clip(RoundedCornerShape(5.dp))
+                .background(tint),
+        )
+        Text(
+            text = label,
+            style = MaterialTheme.typography.bodySmall,
+            color = TextSecondary,
+            modifier = Modifier.padding(start = 6.dp),
+        )
+    }
+}
+
+/** 指标类型 → 标题字符串资源。文案的唯一来源是 `strings.xml`（ledger Ruling R3）。 */
+@Composable
+private fun metricTitleRes(type: MetricType): Int = when (type) {
+    MetricType.STEP -> R.string.metric_step
+    MetricType.HEART_RATE -> R.string.metric_heart_rate
+    MetricType.SLEEP -> R.string.metric_sleep
+    MetricType.BLOOD_OXYGEN -> R.string.metric_blood_oxygen
+    MetricType.STRESS -> R.string.metric_stress
+    MetricType.TEMPERATURE -> R.string.metric_temperature
+    MetricType.BLOOD_PRESSURE -> R.string.metric_blood_pressure
+}
+
+/** 周/月切换。 */
+@Composable
+private fun RangeSelector(
+    current: DateRange,
+    onSelect: (DateRange) -> Unit,
+    modifier: Modifier = Modifier,
+) {
+    Row(
+        modifier = modifier.fillMaxWidth(),
+        horizontalArrangement = Arrangement.spacedBy(8.dp),
+    ) {
+        FilterChip(
+            selected = current == DateRange.WEEK,
+            onClick = { onSelect(DateRange.WEEK) },
+            label = { Text(stringResource(R.string.detail_range_week)) },
+        )
+        FilterChip(
+            selected = current == DateRange.MONTH,
+            onClick = { onSelect(DateRange.MONTH) },
+            label = { Text(stringResource(R.string.detail_range_month)) },
+        )
+    }
+}
+
+/** 一行统计摘要。 */
+@Composable
+private fun StatLine(label: String, value: Double, modifier: Modifier = Modifier) {
+    Row(
+        modifier = modifier.fillMaxWidth().padding(vertical = 4.dp),
+        horizontalArrangement = Arrangement.SpaceBetween,
+    ) {
+        Text(text = label, style = MaterialTheme.typography.bodyMedium, color = TextSecondary)
+        // 数值格式化一律走 core/common/Formatters.kt（Step 1c），页面里不写 String.format：
+        // 那是格式串副本，改口径时要满仓库找。
+        Text(text = formatDecimal(value), style = MaterialTheme.typography.bodyMedium)
+    }
+}
+
+/** 空列表时返回 0.0，避免 NaN。 */
+private fun List<Double>.averageOrZero(): Double = if (isEmpty()) 0.0 else average()
+
+/**
+ * Preview 用的样例数据：7 个点、每天一个、值从 `base` 起小幅递增。
+ * 取值贴近区间下限，好让柱状图有高低差、统计摘要的三行数字不相等（都相等就看不出渲染问题）。
+ */
+private fun previewPoints(base: Double): List<MetricPoint> {
+    val dayMillis = 24L * 60 * 60 * 1000
+    val start = 1_700_000_000_000L
+    return List(7) { index -> MetricPoint(timestamp = start + index * dayMillis, value = base + index * 12) }
+}
+
+/**
+ * 睡眠指标的详情页预览：走 `metric == SLEEP` 分支，带分期卡片。
+ * 取 SLEEP 不是随便挑的 —— 睡眠是唯一有专属区块的指标，预览它才能看见 `SleepStagesCard`。
+ */
+@Preview(showBackground = true)
+@Composable
+private fun MetricDetailContentSleepPreview() {
+    RingHealthTheme {
+        MetricDetailContent(
+            state = MetricDetailUiState(
+                loading = false,
+                metric = MetricType.SLEEP,
+                range = DateRange.WEEK,
+                points = previewPoints(base = 420.0), // 睡眠时长（分钟），与 Mock 的 330~510 同量级
+            ),
+            onBack = {},
+            onSelectRange = {},
+        )
+    }
+}
+
+/**
+ * 非睡眠指标的详情页预览：走「只有趋势图 + 统计摘要」的分支。
+ * 两个 Preview 各覆盖一个分支，是因为只看睡眠那个无法发现「分期卡片漏判 metric、所有指标都显示」这类回归。
+ */
+@Preview(showBackground = true)
+@Composable
+private fun MetricDetailContentStepsPreview() {
+    RingHealthTheme {
+        MetricDetailContent(
+            state = MetricDetailUiState(
+                loading = false,
+                metric = MetricType.STEP,
+                range = DateRange.WEEK,
+                points = previewPoints(base = 7500.0), // 步数，与 Mock 的 3000~12000 同量级
+            ),
+            onBack = {},
+            onSelectRange = {},
+        )
     }
 }

app/src/main/java/com/placeholder/ringhealth/feature/detail/MetricDetailViewModel.kt

@@ -0,0 +1,82 @@
+package com.placeholder.ringhealth.feature.detail
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.ViewModelProvider
+import androidx.lifecycle.viewModelScope
+import androidx.lifecycle.viewmodel.initializer
+import androidx.lifecycle.viewmodel.viewModelFactory
+import com.placeholder.ringhealth.domain.model.DateRange
+import com.placeholder.ringhealth.domain.model.MetricPoint
+import com.placeholder.ringhealth.domain.model.MetricType
+import com.placeholder.ringhealth.domain.repository.HealthDataRepository
+import com.placeholder.ringhealth.ringHealthApplication
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.flatMapLatest
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.stateIn
+import kotlinx.coroutines.flow.update
+
+/** 指标详情 UI 状态。 */
+data class MetricDetailUiState(
+    val loading: Boolean,
+    val metric: MetricType,
+    val range: DateRange,
+    val points: List<MetricPoint>,
+)
+
+/**
+ * 指标详情 ViewModel。因需要指标参数，使用独立工厂创建。
+ */
+@OptIn(ExperimentalCoroutinesApi::class)
+class MetricDetailViewModel(
+    private val metric: MetricType,
+    healthDataRepository: HealthDataRepository,
+) : ViewModel() {
+
+    private val range = MutableStateFlow(DateRange.WEEK)
+
+    val uiState: StateFlow<MetricDetailUiState> = range
+        .flatMapLatest { currentRange ->
+            healthDataRepository.observeMetricHistory(metric, currentRange)
+                .map { points ->
+                    MetricDetailUiState(
+                        loading = false,
+                        metric = metric,
+                        range = currentRange,
+                        points = points,
+                    )
+                }
+        }
+        .stateIn(
+            scope = viewModelScope,
+            started = SharingStarted.WhileSubscribed(STOP_TIMEOUT_MILLIS),
+            initialValue = MetricDetailUiState(
+                loading = true,
+                metric = metric,
+                range = DateRange.WEEK,
+                points = emptyList(),
+            ),
+        )
+
+    /** 切换时间范围（周/月）。 */
+    fun switchRange(newRange: DateRange) {
+        range.update { newRange }
+    }
+
+    companion object {
+        private const val STOP_TIMEOUT_MILLIS = 5_000L
+
+        /** 为指定指标构造 ViewModel 工厂。 */
+        fun factory(metric: MetricType): ViewModelProvider.Factory = viewModelFactory {
+            initializer {
+                MetricDetailViewModel(
+                    metric = metric,
+                    healthDataRepository = ringHealthApplication().container.healthDataRepository,
+                )
+            }
+        }
+    }
+}

app/src/main/res/values/strings.xml

@@ -67,4 +67,18 @@
     <string name="profile_check_update_desc">当前版本 0.1.0</string>
     <string name="profile_help">帮助与反馈</string>
     <string name="profile_help_desc">常见问题与意见反馈</string>
+
+    <string name="detail_range_week">近 7 天</string>
+    <string name="detail_range_month">近 30 天</string>
+    <string name="detail_average">平均</string>
+    <string name="detail_max">最高</string>
+    <string name="detail_min">最低</string>
+    <string name="detail_trend">趋势</string>
+    <string name="detail_sleep_stages">睡眠分期</string>
+    <string name="detail_sleep_deep">深睡</string>
+    <string name="detail_sleep_light">浅睡</string>
+    <string name="detail_sleep_awake">清醒</string>
+    <string name="detail_sleep_fall_asleep">入睡时间</string>
+    <string name="detail_sleep_wake_up">起床时间</string>
+    <string name="action_back">返回</string>
 </resources>

app/src/test/java/com/placeholder/ringhealth/core/common/FormattersTest.kt

@@ -39,6 +39,13 @@ class FormattersTest {
         assertEquals("1,234", formatCalories(1234))
     }
 
+    @Test
+    fun `formatDecimal 保留一位小数`() {
+        assertEquals("72.0", formatDecimal(72.0))
+        assertEquals("98.6", formatDecimal(98.56))
+        assertEquals("0.0", formatDecimal(0.0))
+    }
+
     @Test
     fun `stressLevelLabelRes 按区间映射到对应字符串资源`() {
         assertEquals(R.string.stress_relaxed, stressLevelLabelRes(20))

app/src/test/java/com/placeholder/ringhealth/core/navigation/RoutesTest.kt

@@ -0,0 +1,25 @@
+package com.placeholder.ringhealth.core.navigation
+
+import com.placeholder.ringhealth.domain.model.MetricType
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/** 路由表的一致性测试：模板与实际拼出的路由必须始终吻合（ledger Ruling R22）。 */
+class RoutesTest {
+
+    @Test
+    fun `detail 拼出的路由能被详情模板匹配`() {
+        val expectedPrefix = Routes.DETAIL_PATTERN.substringBefore("{")
+        MetricType.entries.forEach { metric ->
+            val route = Routes.detail(metric)
+            assertTrue("$route 不以 $expectedPrefix 开头", route.startsWith(expectedPrefix))
+            assertEquals(metric.name, route.removePrefix(expectedPrefix))
+        }
+    }
+
+    @Test
+    fun `占位符名与参数常量一致`() {
+        assertTrue(Routes.DETAIL_PATTERN.contains("{${Routes.DETAIL_ARG_METRIC}}"))
+    }
+}

app/src/test/java/com/placeholder/ringhealth/feature/detail/MetricDetailViewModelTest.kt

@@ -0,0 +1,83 @@
+package com.placeholder.ringhealth.feature.detail
+
+import com.placeholder.ringhealth.data.mock.MockHealthDataRepository
+import com.placeholder.ringhealth.domain.model.DateRange
+import com.placeholder.ringhealth.domain.model.MetricType
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.advanceUntilIdle
+import kotlinx.coroutines.test.resetMain
+import kotlinx.coroutines.test.runTest
+import kotlinx.coroutines.test.setMain
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Before
+import org.junit.Test
+
+/** 指标详情 ViewModel 测试。 */
+@OptIn(ExperimentalCoroutinesApi::class)
+class MetricDetailViewModelTest {
+
+    private val dispatcher = StandardTestDispatcher()
+
+    @Before
+    fun setUp() {
+        Dispatchers.setMain(dispatcher)
+    }
+
+    @After
+    fun tearDown() {
+        Dispatchers.resetMain()
+    }
+
+    @Test
+    fun `默认输出近 7 天的数据`() = runTest(dispatcher) {
+        val viewModel = MetricDetailViewModel(MetricType.HEART_RATE, MockHealthDataRepository())
+        backgroundScope.launch { viewModel.uiState.collect {} }
+
+        advanceUntilIdle()
+
+        val state = viewModel.uiState.value
+        assertFalse(state.loading)
+        assertEquals(MetricType.HEART_RATE, state.metric)
+        assertEquals(DateRange.WEEK, state.range)
+        assertEquals(7, state.points.size)
+    }
+
+    @Test
+    fun `switchRange 切到月度后变成 30 个点`() = runTest(dispatcher) {
+        val viewModel = MetricDetailViewModel(MetricType.HEART_RATE, MockHealthDataRepository())
+        backgroundScope.launch { viewModel.uiState.collect {} }
+        advanceUntilIdle()
+
+        viewModel.switchRange(DateRange.MONTH)
+        advanceUntilIdle()
+
+        val state = viewModel.uiState.value
+        // 三个断言缺一不可：只断言点数，无法发现「上游没重新订阅、只是把旧数据换了标签」；
+        // 只断言 range，无法发现 flatMapLatest 没生效。
+        assertEquals(DateRange.MONTH, state.range)
+        assertEquals(30, state.points.size)
+        assertEquals(MetricType.HEART_RATE, state.metric)
+
+        viewModel.switchRange(DateRange.WEEK)
+        advanceUntilIdle()
+        assertEquals(7, viewModel.uiState.value.points.size)
+    }
+
+    @Test
+    fun `构造时传入的 metric 被原样带进状态`() = runTest(dispatcher) {
+        // 名字就叫它断言的事，不要写成「标题映射不同」——`metricTitleRes` 是 @Composable，
+        // JVM 测试里根本调不了，那样命名会让人以为这里验了标题映射（其实没有，
+        // 映射本身由 `when` 的穷尽性在编译期保证）。本用例只锁「metric 被原样带进状态」。
+        val viewModel = MetricDetailViewModel(MetricType.SLEEP, MockHealthDataRepository())
+        backgroundScope.launch { viewModel.uiState.collect {} }
+
+        advanceUntilIdle()
+
+        assertEquals(MetricType.SLEEP, viewModel.uiState.value.metric)
+    }
+}