diff --git a/.github/workflows/gradle.yml b/.github/workflows/gradle.yml
new file mode 100644
index 0000000..e824a5e
--- /dev/null
+++ b/.github/workflows/gradle.yml
@@ -0,0 +1,21 @@
+name: Java CI with Gradle
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    if: ${{ github.event_name != 'pull_request' || github.repository != github.event.pull_request.head.repo.full_name }}
+    runs-on: ubuntu-22.04
+    steps:
+    - name: Checkout Repository
+      uses: actions/checkout@v4
+    - name: Validate Gradle Wrapper
+      uses: gradle/wrapper-validation-action@v1
+    - name: Set up JDK 17
+      uses: actions/setup-java@v4
+      with:
+        distribution: 'temurin'
+        java-version: 17
+        check-latest: true
+    - name: Build and test with Gradle
+      run: ./gradlew test
diff --git a/build.gradle.kts b/build.gradle.kts
index f4a3707..a50e216 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -12,10 +12,13 @@ dependencies {
     api("com.google.code.gson:gson:2.10.1")
     api("com.viaversion:nbt:3.0.0")
     api("it.unimi.dsi:fastutil:8.5.12")
-    api("ch.qos.logback:logback-classic:1.4.6")
+    api("ch.qos.logback:logback-classic:1.4.14")
     compileOnly("org.jetbrains:annotations:24.0.1")
     // Uncomment to manually run mappings gen in ide
     // compileOnly(files("server.jar"))
+
+    testImplementation("org.junit.jupiter:junit-jupiter:5.10.1")
+    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
 }
 
 group = "com.viaversion"
@@ -70,4 +73,8 @@ tasks {
     build {
         dependsOn(shadowJar)
     }
+
+    test {
+        useJUnitPlatform()
+    }
 }
diff --git a/mappings/diff/mapping-1.14to1.15.json b/mappings/diff/mapping-1.14to1.15.json
index 59ed5f1..033049a 100644
--- a/mappings/diff/mapping-1.14to1.15.json
+++ b/mappings/diff/mapping-1.14to1.15.json
@@ -16,5 +16,12 @@
     "11211": "bell[attachment=double_wall,facing=south,powered=false]",
     "11212": "bell[attachment=double_wall,facing=west,powered=false]",
     "11213": "bell[attachment=double_wall,facing=east,powered=false]"
+  },
+  "sounds": {
+    "entity.parrot.imitate.enderman": "",
+    "entity.parrot.imitate.panda": "",
+    "entity.parrot.imitate.polar_bear": "",
+    "entity.parrot.imitate.wolf": "",
+    "entity.parrot.imitate.zombie_pigman": ""
   }
 }
\ No newline at end of file
diff --git a/output/backwards/mappings-1.13to1.12.nbt b/output/backwards/mappings-1.13to1.12.nbt
index 6b5d115..e246587 100644
Binary files a/output/backwards/mappings-1.13to1.12.nbt and b/output/backwards/mappings-1.13to1.12.nbt differ
diff --git a/output/mappings-1.12to1.13.nbt b/output/mappings-1.12to1.13.nbt
index 848c5a6..050e321 100644
Binary files a/output/mappings-1.12to1.13.nbt and b/output/mappings-1.12to1.13.nbt differ
diff --git a/src/main/java/com/viaversion/mappingsgenerator/CursedMappings.java b/src/main/java/com/viaversion/mappingsgenerator/CursedMappings.java
index 49d174e..fbf189c 100644
--- a/src/main/java/com/viaversion/mappingsgenerator/CursedMappings.java
+++ b/src/main/java/com/viaversion/mappingsgenerator/CursedMappings.java
@@ -23,27 +23,29 @@ import java.io.IOException;
 public final class CursedMappings {
 
     public static void optimizeAndSaveOhSoSpecial1_12AsNBT() throws IOException {
-        final MappingsOptimizer optimizer = new MappingsOptimizer("1.12", "1.13");
-        optimizer.keepUnknownFields();
-        optimizer.handleUnknownFields();
+        final MappingsOptimizer optimizer = create("1.12", "1.13");
         optimizer.cursedMappings("blocks", "blockstates", "blockstates", 4084);
-        optimizer.cursedMappings("items", "items", "items");
         optimizer.cursedMappings("legacy_enchantments", "enchantments", "enchantments", 72);
-        optimizer.mappings(false, "sounds");
         optimizer.write(MappingsOptimizer.OUTPUT_DIR);
     }
 
     public static void optimizeAndSaveOhSoSpecial1_12AsNBTBackwards() throws IOException {
-        final MappingsOptimizer optimizer = new MappingsOptimizer("1.13", "1.12");
-        optimizer.keepUnknownFields();
-        optimizer.handleUnknownFields();
+        final MappingsOptimizer optimizer = create("1.13", "1.12");
         optimizer.cursedMappings("blockstates", "blocks", "blockstates", 8582);
-        optimizer.cursedMappings("items", "items", "items");
         optimizer.cursedMappings("enchantments", "legacy_enchantments", "enchantments");
         optimizer.names("items", "itemnames");
         optimizer.fullNames("entitynames", "entitynames");
         optimizer.fullNames("sounds", "soundnames");
-        optimizer.mappings(false, "sounds");
         optimizer.write(MappingsOptimizer.OUTPUT_BACKWARDS_DIR);
     }
+
+    private static MappingsOptimizer create(final String from, final String to) throws IOException {
+        final MappingsOptimizer optimizer = new MappingsOptimizer(from, to);
+        optimizer.setErrorStrategy(ErrorStrategy.IGNORE);
+        optimizer.keepUnknownFields();
+        optimizer.handleUnknownFields();
+        optimizer.cursedMappings("items", "items", "items");
+        optimizer.mappings(false, "sounds");
+        return optimizer;
+    }
 }
diff --git a/src/main/java/com/viaversion/mappingsgenerator/ErrorStrategy.java b/src/main/java/com/viaversion/mappingsgenerator/ErrorStrategy.java
new file mode 100644
index 0000000..8fe04f2
--- /dev/null
+++ b/src/main/java/com/viaversion/mappingsgenerator/ErrorStrategy.java
@@ -0,0 +1,40 @@
+/*
+ * This file is part of ViaVersion Mappings - https://github.com/ViaVersion/Mappings
+ * Copyright (C) 2023 Nassim Jahnke
+ * Copyright (C) 2023 ViaVersion and contributors
+ *
+ * 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 <http://www.gnu.org/licenses/>.
+ */
+package com.viaversion.mappingsgenerator;
+
+import java.util.function.Consumer;
+
+public enum ErrorStrategy {
+    IGNORE(message -> {
+    }),
+    WARN(MappingsLoader.LOGGER::warn),
+    ERROR(message -> {
+        throw new RuntimeException(message);
+    });
+
+    private final Consumer<String> action;
+
+    ErrorStrategy(final Consumer<String> action) {
+        this.action = action;
+    }
+
+    public void apply(final String message) {
+        action.accept(message);
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/viaversion/mappingsgenerator/ManualRunner.java b/src/main/java/com/viaversion/mappingsgenerator/ManualRunner.java
index dca5b29..4a3fdbb 100644
--- a/src/main/java/com/viaversion/mappingsgenerator/ManualRunner.java
+++ b/src/main/java/com/viaversion/mappingsgenerator/ManualRunner.java
@@ -25,18 +25,15 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Set;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 public final class ManualRunner {
 
-    private static final Logger LOGGER = LoggerFactory.getLogger(ManualRunner.class.getSimpleName());
     private static final Set<String> SPECIAL_BACKWARDS_ONLY = Set.of("1.9.4", "1.10", "1.11");
     private static final boolean ALL = true;
 
     public static void main(final String[] args) throws IOException {
         if (ALL) {
-            runAll();
+            runAll(ErrorStrategy.WARN);
             return;
         }
 
@@ -52,9 +49,9 @@ public final class ManualRunner {
     }
 
     /**
-     * Runs the optimizer for all mapping files present in the mappings/ directory.
+     * Runs the optimizer for all mapping files present in the 'mappings' directory.
      */
-    public static void runAll() throws IOException {
+    public static void runAll(final ErrorStrategy errorStrategy) throws IOException {
         final List<String> versions = new ArrayList<>();
         for (final File file : MappingsOptimizer.MAPPINGS_DIR.toFile().listFiles()) {
             final String name = file.getName();
@@ -69,7 +66,6 @@ public final class ManualRunner {
         for (int i = 0; i < versions.size() - 1; i++) {
             final String from = versions.get(i);
             final String to = versions.get(i + 1);
-            LOGGER.info("=============================");
             if (from.equals("1.12") && to.equals("1.13")) {
                 CursedMappings.optimizeAndSaveOhSoSpecial1_12AsNBT();
                 CursedMappings.optimizeAndSaveOhSoSpecial1_12AsNBTBackwards();
@@ -78,17 +74,18 @@ public final class ManualRunner {
 
             final boolean special = SPECIAL_BACKWARDS_ONLY.contains(from);
             if (!special) {
-                new MappingsOptimizer(from, to).optimizeAndWrite();
-                LOGGER.info("-----------------------------");
+                final MappingsOptimizer mappingsOptimizer = new MappingsOptimizer(from, to);
+                mappingsOptimizer.setErrorStrategy(errorStrategy);
+                mappingsOptimizer.optimizeAndWrite();
             }
 
             final MappingsOptimizer backwardsOptimizer = new MappingsOptimizer(to, from);
+            backwardsOptimizer.setErrorStrategy(errorStrategy);
             if (special) {
                 backwardsOptimizer.ignoreMissingMappingsFor("sounds");
             }
 
             backwardsOptimizer.optimizeAndWrite();
-            LOGGER.info("");
         }
     }
 
diff --git a/src/main/java/com/viaversion/mappingsgenerator/MappingsLoader.java b/src/main/java/com/viaversion/mappingsgenerator/MappingsLoader.java
index 6657a78..be8f918 100644
--- a/src/main/java/com/viaversion/mappingsgenerator/MappingsLoader.java
+++ b/src/main/java/com/viaversion/mappingsgenerator/MappingsLoader.java
@@ -38,8 +38,8 @@ import org.slf4j.LoggerFactory;
 
 public final class MappingsLoader {
 
+    public static final Logger LOGGER = LoggerFactory.getLogger(MappingsLoader.class.getSimpleName());
     private static final Gson GSON = new GsonBuilder().disableHtmlEscaping().create();
-    private static final Logger LOGGER = LoggerFactory.getLogger(MappingsLoader.class.getSimpleName());
 
     /**
      * Loads and return the json mappings file.
@@ -63,10 +63,10 @@ public final class MappingsLoader {
      * @param unmappedIdentifiers array of unmapped identifiers
      * @param mappedIdentifiers   array of mapped identifiers
      * @param diffIdentifiers     diff identifiers
-     * @param warnOnMissing       whether to warn on missing mappings
+     * @param errorStrategy       whether to warn on missing mappings
      * @return mappings result with int to int array mappings
      */
-    public static MappingsResult map(final JsonArray unmappedIdentifiers, final JsonArray mappedIdentifiers, @Nullable final JsonObject diffIdentifiers, final boolean warnOnMissing) {
+    public static MappingsResult map(final JsonArray unmappedIdentifiers, final JsonArray mappedIdentifiers, @Nullable final JsonObject diffIdentifiers, final ErrorStrategy errorStrategy) {
         final int[] output = new int[unmappedIdentifiers.size()];
         final Object2IntMap<String> mappedIdentifierMap = MappingsLoader.arrayToMap(mappedIdentifiers);
         int emptyMappings = 0;
@@ -74,7 +74,7 @@ public final class MappingsLoader {
         int shiftChanges = 0;
         for (int id = 0; id < unmappedIdentifiers.size(); id++) {
             final JsonElement unmappedIdentifier = unmappedIdentifiers.get(id);
-            final int mappedId = mapEntry(id, unmappedIdentifier.getAsString(), mappedIdentifierMap, diffIdentifiers, warnOnMissing);
+            final int mappedId = mapEntry(id, unmappedIdentifier.getAsString(), mappedIdentifierMap, diffIdentifiers, errorStrategy);
             output[id] = mappedId;
 
             if (mappedId == -1) {
@@ -98,16 +98,16 @@ public final class MappingsLoader {
      * @param unmappedIdentifiers object of unmapped identifiers, keyed by their int id
      * @param mappedIdentifiers   object of mapped identifiers, keyed by their int id
      * @param diffIdentifiers     diff identifiers
-     * @param warnOnMissing       whether to warn on missing mappings
+     * @param errorStrategy       whether to warn on missing mappings
      * @return mappings result
      */
-    public static Int2IntMap map(final JsonObject unmappedIdentifiers, final JsonObject mappedIdentifiers, @Nullable final JsonObject diffIdentifiers, final boolean warnOnMissing) {
+    public static Int2IntMap map(final JsonObject unmappedIdentifiers, final JsonObject mappedIdentifiers, @Nullable final JsonObject diffIdentifiers, final ErrorStrategy errorStrategy) {
         final Int2IntMap output = new Int2IntLinkedOpenHashMap();
         output.defaultReturnValue(-1);
         final Object2IntMap<String> mappedIdentifierMap = MappingsLoader.indexedObjectToMap(mappedIdentifiers);
         for (final Map.Entry<String, JsonElement> entry : unmappedIdentifiers.entrySet()) {
             final int id = Integer.parseInt(entry.getKey());
-            final int mappedId = mapEntry(id, entry.getValue().getAsString(), mappedIdentifierMap, diffIdentifiers, warnOnMissing);
+            final int mappedId = mapEntry(id, entry.getValue().getAsString(), mappedIdentifierMap, diffIdentifiers, errorStrategy);
             output.put(id, mappedId);
         }
         return output;
@@ -120,10 +120,10 @@ public final class MappingsLoader {
      * @param value             value of the entry
      * @param mappedIdentifiers mapped identifiers
      * @param diffIdentifiers   diff identifiers
-     * @param warnOnMissing     whether to warn on missing mappings
+     * @param errorStrategy     whether to warn on missing mappings
      * @return mapped id, or -1 if it was not found
      */
-    private static int mapEntry(final int id, final String value, final Object2IntMap<String> mappedIdentifiers, @Nullable final JsonObject diffIdentifiers, final boolean warnOnMissing) {
+    private static int mapEntry(final int id, final String value, final Object2IntMap<String> mappedIdentifiers, @Nullable final JsonObject diffIdentifiers, final ErrorStrategy errorStrategy) {
         int mappedId = mappedIdentifiers.getInt(value);
         if (mappedId != -1) {
             return mappedId;
@@ -131,9 +131,7 @@ public final class MappingsLoader {
 
         final int dataIndex;
         if (diffIdentifiers == null) {
-            if (warnOnMissing) {
-                LOGGER.warn("No direct mapping or diff file for {} :( ", value);
-            }
+            errorStrategy.apply("No direct mapping or diff file for " + value + " :( ");
             return -1;
         }
 
@@ -167,8 +165,8 @@ public final class MappingsLoader {
             mappedId = mappedIdentifiers.getInt(mappedName);
         }
 
-        if (mappedId == -1 && warnOnMissing) {
-            LOGGER.warn("No diff entry for {} :( ", value);
+        if (mappedId == -1) {
+            errorStrategy.apply("No mapping for " + value + " :( ");
         }
         return mappedId;
     }
@@ -202,7 +200,7 @@ public final class MappingsLoader {
             final JsonObject existingDiffIdentifiers = existingDiffObject != null && existingDiffObject.has(key) ? existingDiffObject.getAsJsonObject(key) : null;
             for (int id = 0; id < unmappedIdentifiers.size(); id++) {
                 final String unmappedIdentifier = unmappedIdentifiers.get(id).getAsString();
-                final int mappedId = mapEntry(id, unmappedIdentifier, mappedIdentifierMap, existingDiffIdentifiers, false);
+                final int mappedId = mapEntry(id, unmappedIdentifier, mappedIdentifierMap, existingDiffIdentifiers, ErrorStrategy.IGNORE);
                 if (mappedId != -1) {
                     continue;
                 }
@@ -281,6 +279,6 @@ public final class MappingsLoader {
      * @param identityMappings number of identity mappings
      * @param shiftChanges     number of shift changes where a mapped id is not the last mapped id + 1
      */
-    record MappingsResult(int[] mappings, int mappedSize, int emptyMappings, int identityMappings, int shiftChanges) {
+    public record MappingsResult(int[] mappings, int mappedSize, int emptyMappings, int identityMappings, int shiftChanges) {
     }
 }
diff --git a/src/main/java/com/viaversion/mappingsgenerator/MappingsOptimizer.java b/src/main/java/com/viaversion/mappingsgenerator/MappingsOptimizer.java
index 43c7ef6..9a57338 100644
--- a/src/main/java/com/viaversion/mappingsgenerator/MappingsOptimizer.java
+++ b/src/main/java/com/viaversion/mappingsgenerator/MappingsOptimizer.java
@@ -87,6 +87,7 @@ public final class MappingsOptimizer {
     private final String toVersion;
     private final JsonObject unmappedObject;
     private final JsonObject mappedObject;
+    private ErrorStrategy errorStrategy = ErrorStrategy.WARN;
     private JsonObject diffObject;
     private boolean keepUnknownFields;
 
@@ -143,7 +144,7 @@ public final class MappingsOptimizer {
      * Optimizes mapping files as nbt files with only the necessary data (int to int mappings in form of int arrays).
      */
     public void optimizeAndWrite() throws IOException {
-        LOGGER.info("Compacting json mapping files for versions {} → {}...", fromVersion, toVersion);
+        LOGGER.info("=== Compacting json mapping files for versions {} → {}...", fromVersion, toVersion);
 
         if (keepUnknownFields) {
             handleUnknownFields();
@@ -244,7 +245,8 @@ public final class MappingsOptimizer {
                 continue;
             }
 
-            LOGGER.warn("NON-STANDARD FIELD: {} - writing it to the file without changes", key);
+            errorStrategy.apply("NON-STANDARD FIELD: " + key + " - writing it to the file without changes");
+
             final Tag asTag = JsonConverter.toTag(unmappedObject.get(key));
             output.put(key, asTag);
         }
@@ -275,8 +277,8 @@ public final class MappingsOptimizer {
         serialize(result, output, key, alwaysWriteIdentity);
     }
 
-    private boolean shouldWarn(final String key) {
-        return !ignoreMissing.contains(key);
+    private ErrorStrategy shouldWarn(final String key) {
+        return ignoreMissing.contains(key) ? ErrorStrategy.IGNORE : errorStrategy;
     }
 
     public void cursedMappings(final String unmappedKey, final String mappedKey, final String outputKey) {
@@ -295,7 +297,7 @@ public final class MappingsOptimizer {
                 JsonConverter.toJsonObject(unmappedObject.get(unmappedKey)),
                 mappedIdentifiers,
                 diffObject != null ? diffObject.getAsJsonObject(unmappedKey) : null,
-                true
+                errorStrategy
         );
 
         final CompoundTag changedTag = new CompoundTag();
@@ -560,4 +562,8 @@ public final class MappingsOptimizer {
         // One entry in two arrays each time the id is not shifted by 1 from the last id + more approximate length for extra tags
         return result.shiftChanges() * 2 + 10;
     }
+
+    public void setErrorStrategy(final ErrorStrategy errorStrategy) {
+        this.errorStrategy = errorStrategy;
+    }
 }
diff --git a/src/test/java/com/viaversion/mappingsgenerator/MappingsTest.java b/src/test/java/com/viaversion/mappingsgenerator/MappingsTest.java
new file mode 100644
index 0000000..fd27705
--- /dev/null
+++ b/src/test/java/com/viaversion/mappingsgenerator/MappingsTest.java
@@ -0,0 +1,12 @@
+package com.viaversion.mappingsgenerator;
+
+import java.io.IOException;
+import org.junit.jupiter.api.Test;
+
+public class MappingsTest {
+
+    @Test
+    void testFilledStatus() throws IOException {
+        ManualRunner.runAll(ErrorStrategy.ERROR);
+    }
+}