diff --git a/build.gradle b/build.gradle
index 7397719..b625ffd 100644
--- a/build.gradle
+++ b/build.gradle
@@ -62,6 +62,16 @@ sourceSets {
             exclude '**/*.java', '**/*.kt'
         }
     }
+
+    test {
+        java {
+            srcDirs = ['testsrc']
+        }
+        resources {
+            srcDirs = ['testsrc']
+            exclude '**/*.java', '**/*.kt'
+        }
+    }
 }
 
 repositories {
@@ -73,6 +83,9 @@ dependencies {
     testCompileOnly 'org.projectlombok:lombok:1.18.22'
     annotationProcessor 'org.projectlombok:lombok:1.18.22'
     testAnnotationProcessor 'org.projectlombok:lombok:1.18.22'
+
+    testImplementation 'junit:junit:4.13.2'
+    testImplementation 'org.hamcrest:hamcrest:2.2'
 }
 
 task buildProject {
diff --git a/src/de/steamwar/command/SWCommandUtils.java b/src/de/steamwar/command/SWCommandUtils.java
index 52e1d75..4a6088a 100644
--- a/src/de/steamwar/command/SWCommandUtils.java
+++ b/src/de/steamwar/command/SWCommandUtils.java
@@ -21,7 +21,11 @@ public class SWCommandUtils {
     private final Map<String, AbstractGuardChecker<?>> GUARD_FUNCTIONS = new HashMap<>();
 
     static {
-        addMapper(boolean.class, Boolean.class, createMapper(Boolean::parseBoolean, s -> Arrays.asList("true", "false")));
+        addMapper(boolean.class, Boolean.class, createMapper(s -> {
+            if (s.equalsIgnoreCase("true")) return true;
+            if (s.equalsIgnoreCase("false")) return false;
+            return null;
+        }, s -> Arrays.asList("true", "false")));
         addMapper(float.class, Float.class, createMapper(numberMapper(Float::parseFloat), numberCompleter(Float::parseFloat)));
         addMapper(double.class, Double.class, createMapper(numberMapper(Double::parseDouble), numberCompleter(Double::parseDouble)));
         addMapper(int.class, Integer.class, createMapper(numberMapper(Integer::parseInt), numberCompleter(Integer::parseInt)));
diff --git a/src/de/steamwar/command/SubCommand.java b/src/de/steamwar/command/SubCommand.java
index 4b9a4a6..2f41791 100644
--- a/src/de/steamwar/command/SubCommand.java
+++ b/src/de/steamwar/command/SubCommand.java
@@ -4,6 +4,7 @@ import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.lang.reflect.Parameter;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.function.Function;
diff --git a/testsrc/de/steamwar/command/ArgumentCommand.java b/testsrc/de/steamwar/command/ArgumentCommand.java
new file mode 100644
index 0000000..c630a93
--- /dev/null
+++ b/testsrc/de/steamwar/command/ArgumentCommand.java
@@ -0,0 +1,41 @@
+package de.steamwar.command;
+
+import de.steamwar.command.dto.ExecutionIdentifier;
+import de.steamwar.command.dto.TestSWCommand;
+
+public class ArgumentCommand extends TestSWCommand {
+
+    public ArgumentCommand() {
+        super("argument");
+    }
+
+    @Register
+    public void argument(String sender, boolean b, boolean b2) {
+        throw new ExecutionIdentifier("RunArgument with Boolean");
+    }
+
+    @Register
+    public void argument(String sender, float f, float f2, float f3) {
+        throw new ExecutionIdentifier("RunArgument with Float");
+    }
+
+    @Register
+    public void argument(String sender, double d, double d2) {
+        throw new ExecutionIdentifier("RunArgument with Double");
+    }
+
+    @Register
+    public void argument(String sender, int i) {
+        throw new ExecutionIdentifier("RunArgument with Integer");
+    }
+
+    @Register
+    public void argument(String sender, long l, long l2) {
+        throw new ExecutionIdentifier("RunArgument with Long");
+    }
+
+    @Register
+    public void argument(String sender, String arg) {
+        throw new ExecutionIdentifier("RunArgument with String");
+    }
+}
diff --git a/testsrc/de/steamwar/command/ArgumentCommandTest.java b/testsrc/de/steamwar/command/ArgumentCommandTest.java
new file mode 100644
index 0000000..d7a24f1
--- /dev/null
+++ b/testsrc/de/steamwar/command/ArgumentCommandTest.java
@@ -0,0 +1,87 @@
+package de.steamwar.command;
+
+import de.steamwar.command.dto.ExecutionIdentifier;
+import org.junit.Test;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.instanceOf;
+import static org.hamcrest.Matchers.is;
+
+public class ArgumentCommandTest {
+
+    @Test
+    public void testNoArgs() {
+        ArgumentCommand cmd = new ArgumentCommand();
+        try {
+            cmd.execute("test", "", new String[0]);
+        } catch (Exception e) {
+            throw new AssertionError("No exception expected");
+        }
+    }
+
+    @Test
+    public void testBoolean() {
+        ArgumentCommand cmd = new ArgumentCommand();
+        try {
+            cmd.execute("test", "", new String[]{"true", "false"});
+        } catch (Exception e) {
+            assertThat(e.getCause().getCause(), is(instanceOf(ExecutionIdentifier.class)));
+            assertThat(e.getCause().getCause().getMessage(), is("RunArgument with Boolean"));
+        }
+    }
+
+    @Test
+    public void testFloat() {
+        ArgumentCommand cmd = new ArgumentCommand();
+        try {
+            cmd.execute("test", "", new String[]{"0.0", "0.0", "0.0"});
+        } catch (Exception e) {
+            assertThat(e.getCause().getCause(), is(instanceOf(ExecutionIdentifier.class)));
+            assertThat(e.getCause().getCause().getMessage(), is("RunArgument with Float"));
+        }
+    }
+
+    @Test
+    public void testDouble() {
+        ArgumentCommand cmd = new ArgumentCommand();
+        try {
+            cmd.execute("test", "", new String[]{"0.0", "0.0"});
+        } catch (Exception e) {
+            assertThat(e.getCause().getCause(), is(instanceOf(ExecutionIdentifier.class)));
+            assertThat(e.getCause().getCause().getMessage(), is("RunArgument with Double"));
+        }
+    }
+
+    @Test
+    public void testInt() {
+        ArgumentCommand cmd = new ArgumentCommand();
+        try {
+            cmd.execute("test", "", new String[]{"0"});
+        } catch (Exception e) {
+            assertThat(e.getCause().getCause(), is(instanceOf(ExecutionIdentifier.class)));
+            assertThat(e.getCause().getCause().getMessage(), is("RunArgument with Integer"));
+        }
+    }
+
+    @Test
+    public void testLong() {
+        ArgumentCommand cmd = new ArgumentCommand();
+        try {
+            cmd.execute("test", "", new String[]{"0", "0"});
+        } catch (Exception e) {
+            assertThat(e.getCause().getCause(), is(instanceOf(ExecutionIdentifier.class)));
+            assertThat(e.getCause().getCause().getMessage(), is("RunArgument with Long"));
+        }
+    }
+
+    @Test
+    public void testString() {
+        ArgumentCommand cmd = new ArgumentCommand();
+        try {
+            cmd.execute("test", "", new String[]{"Hello World"});
+        } catch (Exception e) {
+            assertThat(e.getCause().getCause(), is(instanceOf(ExecutionIdentifier.class)));
+            assertThat(e.getCause().getCause().getMessage(), is("RunArgument with String"));
+        }
+    }
+}
diff --git a/testsrc/de/steamwar/command/SimpleCommand.java b/testsrc/de/steamwar/command/SimpleCommand.java
new file mode 100644
index 0000000..88d0bd6
--- /dev/null
+++ b/testsrc/de/steamwar/command/SimpleCommand.java
@@ -0,0 +1,16 @@
+package de.steamwar.command;
+
+import de.steamwar.command.dto.ExecutionIdentifier;
+import de.steamwar.command.dto.TestSWCommand;
+
+public class SimpleCommand extends TestSWCommand {
+
+    public SimpleCommand() {
+        super("simple");
+    }
+
+    @Register
+    public void simple(String s) {
+        throw new ExecutionIdentifier("RunSimple with noArgs");
+    }
+}
diff --git a/testsrc/de/steamwar/command/SimpleCommandTest.java b/testsrc/de/steamwar/command/SimpleCommandTest.java
new file mode 100644
index 0000000..a039e75
--- /dev/null
+++ b/testsrc/de/steamwar/command/SimpleCommandTest.java
@@ -0,0 +1,32 @@
+package de.steamwar.command;
+
+import de.steamwar.command.dto.ExecutionIdentifier;
+import org.junit.Test;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.instanceOf;
+import static org.hamcrest.Matchers.is;
+
+public class SimpleCommandTest {
+
+    @Test
+    public void testSimpleParsing() {
+        SimpleCommand cmd = new SimpleCommand();
+        try {
+            cmd.execute("test", "", new String[0]);
+        } catch (CommandFrameworkException e) {
+            assertThat(e.getCause().getCause(), is(instanceOf(ExecutionIdentifier.class)));
+            assertThat(e.getCause().getCause().getMessage(), is("RunSimple with noArgs"));
+        }
+    }
+
+    @Test
+    public void testSimpleParsingNoResult() {
+        SimpleCommand cmd = new SimpleCommand();
+        try {
+            cmd.execute("test", "", new String[]{"Hello"});
+        } catch (CommandFrameworkException e) {
+            throw new AssertionError("No exception expected");
+        }
+    }
+}
diff --git a/testsrc/de/steamwar/command/dto/ExecutionIdentifier.java b/testsrc/de/steamwar/command/dto/ExecutionIdentifier.java
new file mode 100644
index 0000000..bde7122
--- /dev/null
+++ b/testsrc/de/steamwar/command/dto/ExecutionIdentifier.java
@@ -0,0 +1,7 @@
+package de.steamwar.command.dto;
+
+public class ExecutionIdentifier extends RuntimeException {
+    public ExecutionIdentifier(String message) {
+        super(message);
+    }
+}
diff --git a/testsrc/de/steamwar/command/dto/TestGuardChecker.java b/testsrc/de/steamwar/command/dto/TestGuardChecker.java
new file mode 100644
index 0000000..ff38ebc
--- /dev/null
+++ b/testsrc/de/steamwar/command/dto/TestGuardChecker.java
@@ -0,0 +1,6 @@
+package de.steamwar.command.dto;
+
+import de.steamwar.command.AbstractGuardChecker;
+
+public interface TestGuardChecker extends AbstractGuardChecker<String> {
+}
diff --git a/testsrc/de/steamwar/command/dto/TestSWCommand.java b/testsrc/de/steamwar/command/dto/TestSWCommand.java
new file mode 100644
index 0000000..9081000
--- /dev/null
+++ b/testsrc/de/steamwar/command/dto/TestSWCommand.java
@@ -0,0 +1,40 @@
+package de.steamwar.command.dto;
+
+import de.steamwar.command.AbstractSWCommand;
+import de.steamwar.command.CommandFrameworkException;
+
+import java.util.function.Supplier;
+
+public class TestSWCommand extends AbstractSWCommand<String> {
+
+    protected TestSWCommand(String command) {
+        super(String.class, command);
+    }
+
+    protected TestSWCommand(String command, String[] aliases) {
+        super(String.class, command, aliases);
+    }
+
+    @Override
+    protected void createAndSafeCommand(String command, String[] aliases) {
+
+    }
+
+    @Override
+    public void unregister() {
+
+    }
+
+    @Override
+    public void register() {
+
+    }
+
+    @Override
+    protected void commandSystemError(String sender, CommandFrameworkException e) {
+    }
+
+    @Override
+    protected void commandSystemWarning(Supplier<String> message) {
+    }
+}
diff --git a/testsrc/de/steamwar/command/dto/TestTypeChecker.java b/testsrc/de/steamwar/command/dto/TestTypeChecker.java
new file mode 100644
index 0000000..42a7933
--- /dev/null
+++ b/testsrc/de/steamwar/command/dto/TestTypeChecker.java
@@ -0,0 +1,6 @@
+package de.steamwar.command.dto;
+
+import de.steamwar.command.AbstractTypeMapper;
+
+public interface TestTypeChecker<T> extends AbstractTypeMapper<String, T> {
+}