[fenix] For https://github.com/mozilla-mobile/fenix/issues/6464: Add ReleaseChannel test to document assumptions.

app/src/test/java/org/mozilla/fenix/ReleaseChannelTest.kt

@@ -0,0 +1,34 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.fenix
+
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import org.mozilla.fenix.ReleaseChannel.FenixDebug
+
+class ReleaseChannelTest {
+
+    @Test
+    fun `isReleased and isDebug channels are mutually exclusive`() {
+        val debugChannels = setOf(
+            FenixDebug
+        )
+
+        val nonDebugChannels = ReleaseChannel.values().toSet() - debugChannels
+
+        nonDebugChannels.forEach {
+            val className = it.javaClass.simpleName
+            assertTrue(className, it.isReleased)
+            assertFalse(className, it.isDebug)
+        }
+
+        debugChannels.forEach {
+            val className = it.javaClass.simpleName
+            assertFalse(className, it.isReleased)
+            assertTrue(className, it.isDebug)
+        }
+    }
+}