WIP DON'T MERGE Add a test for missing string documentation

THIS IS SUPPOSED TO FAIL AT THE MOMENT.

Documentation for all the strings is already written
in translatewiki (see #6457), but not yet imported into GitHub,
so it's supposed to fail now, which is good because you shouldn't trust
tests that never failed :)

Once all the documentation strings are imported, this pull request
should be rebased, and then it's supposed to pass.

The extra string in values-qq/string.xml is also there
just to check that it fails as it should, and will be removed.

Resolves #6485.

Author: amire80

app/src/test/kotlin/resources/StringsDocumentationTest.kt

@@ -0,0 +1,60 @@
+package resources
+
+import org.junit.Test
+import org.junit.Assert.assertTrue
+import org.w3c.dom.Element
+import java.io.File
+import javax.xml.parsers.DocumentBuilderFactory
+
+class StringsDocumentationTest {
+
+    @Test
+    fun `string resources and qq documentation are in sync`() {
+        val projectRoot = File(System.getProperty("user.dir") ?: ".")
+        val sourceFile = File(projectRoot, "src/main/res/values/strings.xml")
+        val docFile = File(projectRoot, "src/main/res/values-qq/strings.xml")
+
+        assertTrue("Source strings.xml not found", sourceFile.exists())
+        assertTrue("Documentation strings.xml (qq) not found", docFile.exists())
+
+        val sourceKeys = parseStringKeys(sourceFile)
+        val docKeys = parseStringKeys(docFile)
+
+        val extraDocs = docKeys - sourceKeys
+
+        assertTrue(
+            "Documentation exists for ${extraDocs.size} non-existent string(s): " +
+                    extraDocs.joinToString(", "),
+            extraDocs.isEmpty()
+        )
+
+        val missingDocs = sourceKeys - docKeys
+
+        assertTrue(
+            "Missing documentation for ${missingDocs.size} string(s): " +
+                    missingDocs.joinToString(", "),
+            missingDocs.isEmpty()
+        )
+    }
+
+    private fun parseStringKeys(file: File): Set<String> {
+        val factory = DocumentBuilderFactory.newInstance()
+        val builder = factory.newDocumentBuilder()
+        val doc = builder.parse(file)
+
+        val keys = mutableSetOf<String>()
+
+        listOf("string", "plurals").forEach { tagName ->
+            val elements = doc.getElementsByTagName(tagName)
+            for (i in 0 until elements.length) {
+                val element = elements.item(i) as Element
+                val name = element.getAttribute("name")
+                if (name.isNotEmpty()) {
+                    keys.add(name)
+                }
+            }
+        }
+
+        return keys
+    }
+}