Add test that translation files follow the rules

src/main/resources/assets/clientcommands/lang/en_us.json

@@ -182,7 +182,7 @@
   "commands.crender.entities.success": "Entity rendering rules have been updated",
 
   "commands.creply.noTargetFound": "Could not find a target to reply to",
-  "commands.creply.messageTooLong": "Your reply was too long (maximum: %d, given: %d)",
+  "commands.creply.messageTooLong": "Your reply was too long (maximum: %s, given: %s)",
 
   "commands.csignsearch.starting": "Searching signs",
 

src/test/java/net/earthcomputer/clientcommands/test/TranslationsTest.java

@@ -0,0 +1,68 @@
+package net.earthcomputer.clientcommands.test;
+
+import com.google.gson.Gson;
+import com.google.gson.JsonObject;
+import net.fabricmc.loader.api.FabricLoader;
+import org.junit.jupiter.api.DynamicTest;
+import org.junit.jupiter.api.TestFactory;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.regex.Pattern;
+import java.util.stream.Stream;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public final class TranslationsTest {
+    private static final Gson GSON = new Gson();
+
+    @TestFactory
+    public Iterable<DynamicTest> testTranslate() throws IOException {
+        Path langDir = FabricLoader.getInstance().getModContainer("clientcommands").orElseThrow()
+            .findPath("assets/clientcommands/lang").orElseThrow();
+
+        JsonObject enUs;
+        try (BufferedReader reader = Files.newBufferedReader(langDir.resolve("en_us.json"))) {
+            enUs = GSON.fromJson(reader, JsonObject.class);
+        }
+
+        List<DynamicTest> tests = new ArrayList<>();
+
+        try (Stream<Path> langFiles = Files.list(langDir)) {
+            for (Path langFile : (Iterable<Path>) langFiles::iterator) {
+                tests.add(DynamicTest.dynamicTest("Check " + langFile.getFileName().toString(), () -> checkLangFile(enUs, langFile)));
+            }
+        }
+
+        return tests;
+    }
+
+    private static void checkLangFile(JsonObject enUs, Path langFile) throws IOException {
+        String langFileName = langFile.getFileName().toString();
+
+        JsonObject lang;
+        try (BufferedReader reader = Files.newBufferedReader(langFile)) {
+            lang = GSON.fromJson(reader, JsonObject.class);
+        }
+
+        for (String key : lang.keySet()) {
+            assertTrue(enUs.has(key), () -> langFileName + " has key " + key + " not present in en_us.json");
+        }
+        for (var entry : lang.entrySet()) {
+            assertTrue(entry.getValue().isJsonPrimitive() && entry.getValue().getAsJsonPrimitive().isString(), () -> langFileName + " has a non-string value associated with " + entry.getKey());
+        }
+        for (var entry : lang.entrySet()) {
+            assertTrue(checkPercentS(entry.getValue().getAsString()), () -> langFileName + " has invalid formatting codes in " + entry.getKey() + ". Only %s, %n$s and %% are allowed");
+        }
+    }
+
+    private static final Pattern NON_PERCENT_S_REGEX = Pattern.compile("%(?!(?:\\d+\\$)?s)");
+
+    private static boolean checkPercentS(String value) {
+        return !NON_PERCENT_S_REGEX.matcher(value.replace("%%", "")).find();
+    }
+}