test(android): cover the DocumentsProvider document-id path logic

Extract the VFS document-id path logic (child/parent/name) into an internal
DocIdLogic object as the single source of truth and add JVM unit tests for it
(runs on the host, no emulator). The cursor-building and openDocument paths
still need Robolectric/an emulator; this covers the fiddly trailing-slash and
root edge cases that are easy to break, and runs in the Android CI job.

Author: Mearman

.github/workflows/ci.yml

@@ -246,6 +246,9 @@ jobs:
       - name: Assemble the debug APK
         working-directory: android
         run: ./gradlew :app:assembleDebug --no-daemon
+      - name: Run JVM unit tests
+        working-directory: android
+        run: ./gradlew :app:testDebugUnitTest --no-daemon
       - name: Upload the debug APK (CI artifact)
         uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:

android/app/build.gradle

@@ -54,4 +54,5 @@ dependencies {
     // UniFFI Kotlin bindings load the native lib through JNA; the Android aar
     // variant bundles the JNI shim JNA itself needs.
     implementation 'net.java.dev.jna:jna:5.14.0@aar'
+    testImplementation 'junit:junit:4.13.2'
 }

android/app/src/main/java/co/mearman/cascade/CascadeDocumentsProvider.kt

@@ -159,15 +159,11 @@ class CascadeDocumentsProvider : DocumentsProvider() {
     }
 
     private fun childDocId(parent: String, name: String): String =
-        if (parent == ROOT_DOC_ID) "/$name" else "$parent/$name"
+        DocIdLogic.childDocId(parent, name)
 
-    private fun parentOf(documentId: String): String {
-        val trimmed = documentId.trimEnd('/')
-        val idx = trimmed.lastIndexOf('/')
-        return if (idx <= 0) ROOT_DOC_ID else trimmed.substring(0, idx)
-    }
+    private fun parentOf(documentId: String): String = DocIdLogic.parentOf(documentId)
 
-    private fun nameOf(documentId: String): String = documentId.trimEnd('/').substringAfterLast('/')
+    private fun nameOf(documentId: String): String = DocIdLogic.nameOf(documentId)
 
     private fun mimeOf(name: String): String {
         val ext = name.substringAfterLast('.', "").lowercase()
@@ -181,3 +177,21 @@ class CascadeDocumentsProvider : DocumentsProvider() {
         signal: CancellationSignal?,
     ) = null
 }
+
+/**
+ * Document-id path logic, extracted so it has a single source of truth and can
+ * be unit-tested on the JVM without an emulator. Document ids are VFS-absolute
+ * paths with the root represented as `/`.
+ */
+internal object DocIdLogic {
+    fun childDocId(parent: String, name: String): String =
+        if (parent == "/") "/$name" else "$parent/$name"
+
+    fun parentOf(documentId: String): String {
+        val trimmed = documentId.trimEnd('/')
+        val idx = trimmed.lastIndexOf('/')
+        return if (idx <= 0) "/" else trimmed.substring(0, idx)
+    }
+
+    fun nameOf(documentId: String): String = documentId.trimEnd('/').substringAfterLast('/')
+}

android/app/src/test/java/co/mearman/cascade/DocIdLogicTest.kt

@@ -0,0 +1,57 @@
+package co.mearman.cascade
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+/**
+ * JVM unit tests for the document-id path logic. These run on the host JVM
+ * (no emulator) because the logic is pure string manipulation over VFS-absolute
+ * paths — the fiddly trailing-slash and root edge cases that are easy to break.
+ */
+class DocIdLogicTest {
+
+    @Test
+    fun childDocId_under_root_gets_leading_slash() {
+        assertEquals("/Documents", DocIdLogic.childDocId("/", "Documents"))
+    }
+
+    @Test
+    fun childDocId_under_nested_parent_joins_with_slash() {
+        assertEquals("/local/Documents/report.txt", DocIdLogic.childDocId("/local/Documents", "report.txt"))
+    }
+
+    @Test
+    fun parentOf_root_is_root() {
+        assertEquals("/", DocIdLogic.parentOf("/"))
+    }
+
+    @Test
+    fun parentOf_top_level_child_is_root() {
+        assertEquals("/", DocIdLogic.parentOf("/local"))
+    }
+
+    @Test
+    fun parentOf_nested_path_strips_last_segment() {
+        assertEquals("/local/Documents", DocIdLogic.parentOf("/local/Documents/report.txt"))
+    }
+
+    @Test
+    fun parentOf_ignores_trailing_slash() {
+        assertEquals("/local", DocIdLogic.parentOf("/local/Documents/"))
+    }
+
+    @Test
+    fun nameOf_root_is_empty() {
+        assertEquals("", DocIdLogic.nameOf("/"))
+    }
+
+    @Test
+    fun nameOf_returns_last_segment() {
+        assertEquals("report.txt", DocIdLogic.nameOf("/local/Documents/report.txt"))
+    }
+
+    @Test
+    fun nameOf_ignores_trailing_slash() {
+        assertEquals("Documents", DocIdLogic.nameOf("/local/Documents/"))
+    }
+}