test: add unit tests for MirrorGenerator and CacheFileLocator (#19)

Add JUnit5 unit tests for the two pure internal logic classes (previously only black-box GradleTestKit functional tests existed):
- MirrorGenerator.mirrorsFor: central-host mirror rewriting (apache <-> repo1 + GCS) with path preservation; non-central and malformed URLs return empty.
- CacheFileLocator.locate/relativePath: group derivation from the URL, repo-prefix stripping (/maven2/), files-2.1 lookup via a @tempdir fixture, and cache-path splitting.
Also wire tasks.test to useJUnitPlatform (previously only functionalTest did). 9 tests, all green locally.

Author: jamesarich

plugin/build.gradle.kts

@@ -78,6 +78,11 @@ tasks {
     }
 }
 
+// Unit tests (plugin/src/test) use JUnit 5, matching the functional-test suite.
+tasks.test {
+    useJUnitPlatform()
+}
+
 gradlePlugin {
     website = "https://github.com/meshtastic/gradle-flatpak-sources"
     vcsUrl = "https://github.com/meshtastic/gradle-flatpak-sources.git"

plugin/src/test/kotlin/org/meshtastic/flatpak/sources/internal/CacheFileLocatorTest.kt

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2026 Meshtastic LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.meshtastic.flatpak.sources.internal
+
+import java.io.File
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+import org.junit.jupiter.api.io.TempDir
+
+class CacheFileLocatorTest {
+
+    @Test
+    fun `locate finds the cached file, deriving the group from the URL and stripping the repo prefix`(
+        @TempDir root: File,
+    ) {
+        // Gradle files-2.1 layout: <group-with-dots>/<artifact>/<version>/<content-sha1>/<filename>
+        val jar = File(root, "org.example/lib/1.0/deadbeefcafe/lib-1.0.jar")
+        jar.parentFile.mkdirs()
+        jar.writeText("artifact bytes")
+
+        // The URL carries a `/maven2/` repo prefix that must be stripped; the group is `org.example`.
+        val found =
+            CacheFileLocator.locate(root, "https://repo1.maven.org/maven2/org/example/lib/1.0/lib-1.0.jar")
+
+        assertEquals(jar.canonicalFile, found?.canonicalFile)
+    }
+
+    @Test
+    fun `locate returns null when filesRoot is not a directory`() {
+        assertNull(
+            CacheFileLocator.locate(File("/no/such/cache/dir"), "https://repo1.maven.org/maven2/a/b/1.0/b-1.0.jar"),
+        )
+    }
+
+    @Test
+    fun `locate returns null when the URL has fewer than three path segments`(@TempDir root: File) {
+        assertNull(CacheFileLocator.locate(root, "https://repo1.maven.org/a/b"))
+    }
+
+    @Test
+    fun `relativePath splits a full cache path into group, artifact, version, sha1 and filename`(@TempDir root: File) {
+        val cacheFile = File(root, "org.example/lib/1.0/deadbeefcafe/lib-1.0.jar")
+
+        assertEquals(
+            listOf("org.example", "lib", "1.0", "deadbeefcafe", "lib-1.0.jar"),
+            CacheFileLocator.relativePath(root, cacheFile),
+        )
+    }
+
+    @Test
+    fun `relativePath returns null for a path with fewer than five components`(@TempDir root: File) {
+        assertNull(CacheFileLocator.relativePath(root, File(root, "a/b/c")))
+    }
+}

plugin/src/test/kotlin/org/meshtastic/flatpak/sources/internal/MirrorGeneratorTest.kt

@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2026 Meshtastic LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.meshtastic.flatpak.sources.internal
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class MirrorGeneratorTest {
+
+    @Test
+    fun `rewrites the repo1 central host to the apache host plus the GCS mirror, preserving the path`() {
+        val mirrors =
+            MirrorGenerator.mirrorsFor("https://repo1.maven.org/maven2/org/example/lib/1.0/lib-1.0.jar")
+
+        assertEquals(
+            listOf(
+                "https://repo.maven.apache.org/maven2/org/example/lib/1.0/lib-1.0.jar",
+                "https://maven-central.storage-download.googleapis.com/maven2/org/example/lib/1.0/lib-1.0.jar",
+            ),
+            mirrors,
+        )
+    }
+
+    @Test
+    fun `rewrites the apache central host to repo1 plus the GCS mirror`() {
+        val mirrors =
+            MirrorGenerator.mirrorsFor("https://repo.maven.apache.org/maven2/a/b/1.0/b-1.0.pom")
+
+        assertEquals(
+            listOf(
+                "https://repo1.maven.org/maven2/a/b/1.0/b-1.0.pom",
+                "https://maven-central.storage-download.googleapis.com/maven2/a/b/1.0/b-1.0.pom",
+            ),
+            mirrors,
+        )
+    }
+
+    @Test
+    fun `returns no mirrors for non-central hosts`() {
+        // Google, JitPack and the Gradle plugin portal have no well-known public mirrors.
+        assertTrue(MirrorGenerator.mirrorsFor("https://jitpack.io/com/github/x/y/1.0/y-1.0.jar").isEmpty())
+        assertTrue(MirrorGenerator.mirrorsFor("https://dl.google.com/dl/android/maven2/a/b/1.0/b.aar").isEmpty())
+        assertTrue(MirrorGenerator.mirrorsFor("https://plugins.gradle.org/m2/p/p.jar").isEmpty())
+    }
+
+    @Test
+    fun `returns no mirrors for a malformed or hostless URL`() {
+        assertTrue(MirrorGenerator.mirrorsFor("not a valid url").isEmpty())
+        assertTrue(MirrorGenerator.mirrorsFor("").isEmpty())
+    }
+}