Navigate explorer back toward project

app/androidApp/src/test/kotlin/com/example/aiapp/FilesNavigationTest.kt

@@ -0,0 +1,33 @@
+package com.example.aiapp
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class FilesNavigationTest {
+    @Test
+    fun `back walks through the common ancestor toward the project`() {
+        val project = "/home/bob/repos/project"
+        assertEquals("/", nextDirectoryToward("/etc", project))
+        assertEquals("/home", nextDirectoryToward("/", project))
+        assertEquals("/home/bob", nextDirectoryToward("/home", project))
+        assertEquals("/home/bob/repos", nextDirectoryToward("/home/bob", project))
+        assertEquals(project, nextDirectoryToward("/home/bob/repos", project))
+        assertEquals(null, nextDirectoryToward(project, project))
+    }
+
+    @Test
+    fun `back leaves a project descendant one directory at a time`() {
+        assertEquals(
+            "/home/bob/repos/project/src",
+            nextDirectoryToward("/home/bob/repos/project/src/main", "/home/bob/repos/project"),
+        )
+    }
+
+    @Test
+    fun `paths inside the machine home use tilde notation`() {
+        assertEquals("~", tildePath("/home/bob", "/home/bob"))
+        assertEquals("~/repos/project", tildePath("/home/bob/repos/project", "/home/bob/"))
+        assertEquals("/home/bobby/project", tildePath("/home/bobby/project", "/home/bob"))
+        assertEquals("/etc", tildePath("/etc", "/home/bob"))
+    }
+}