Clean up and add unit test on Theme.isDark()

libraries/compound/src/main/kotlin/io/element/android/compound/theme/Theme.kt

@@ -18,8 +18,6 @@ enum class Theme {
     Light,
 }
 
-val themes = listOf(Theme.System, Theme.Dark, Theme.Light)
-
 @Composable
 fun Theme.isDark(): Boolean {
     return when (this) {

libraries/compound/src/test/kotlin/io/element/android/compound/theme/ThemeTest.kt

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2025 New Vector Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.compound.theme
+
+import android.content.res.Configuration
+import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.ui.platform.LocalConfiguration
+import app.cash.molecule.RecompositionMode
+import app.cash.molecule.moleculeFlow
+import app.cash.turbine.test
+import com.google.common.truth.Truth.assertThat
+import kotlinx.coroutines.test.runTest
+import org.junit.Test
+
+class ThemeTest {
+    @Test
+    fun `isDark for System dark returns true`() {
+        `isDark for System`(
+            uiMode = Configuration.UI_MODE_NIGHT_YES,
+            expected = true,
+        )
+    }
+
+    @Test
+    fun `isDark for System light return false`() {
+        `isDark for System`(
+            uiMode = Configuration.UI_MODE_NIGHT_NO,
+            expected = false,
+        )
+    }
+
+    fun `isDark for System`(
+        uiMode: Int,
+        expected: Boolean,
+    ) = runTest {
+        moleculeFlow(RecompositionMode.Immediate) {
+            var result: Boolean? = null
+            CompositionLocalProvider(
+                // Let set the system to dark
+                LocalConfiguration provides Configuration().apply {
+                    this.uiMode = uiMode
+                },
+            ) {
+                result = Theme.System.isDark()
+            }
+            result
+        }.test {
+            assertThat(awaitItem()).isEqualTo(expected)
+        }
+    }
+
+    @Test
+    fun `isDark for Light returns false`() = runTest {
+        moleculeFlow(RecompositionMode.Immediate) {
+            Theme.Light.isDark()
+        }.test {
+            assertThat(awaitItem()).isFalse()
+        }
+    }
+
+    @Test
+    fun `isDark for Dark returns true`() = runTest {
+        moleculeFlow(RecompositionMode.Immediate) {
+            Theme.Dark.isDark()
+        }.test {
+            assertThat(awaitItem()).isTrue()
+        }
+    }
+}