diff --git a/build.gradle b/build.gradle
index f0a23cb..32ef767 100644
--- a/build.gradle
+++ b/build.gradle
@@ -1,5 +1,6 @@
 plugins {
     id 'java'
+    id 'jacoco'
 }
 
 project.group = 'ghast'
@@ -49,3 +50,11 @@ dependencies {
 test {
     useJUnitPlatform()
 }
+
+jacoco {
+    toolVersion = '0.8.5'
+}
+
+jacocoTestReport {
+    dependsOn test
+}
diff --git a/src/main/java/ghast/HashMaps.java b/src/main/java/ghast/HashMaps.java
index ae63bcf..1da8d7d 100644
--- a/src/main/java/ghast/HashMaps.java
+++ b/src/main/java/ghast/HashMaps.java
@@ -17,20 +17,20 @@ public final class HashMaps {
     }
 
     public static <K, V> Map<K, V> of(K k1, V v1) {
-        return new HashMap<K, V>() {{
+        return new HashMap<K, V>(1) {{
             put(k1, v1);
         }};
     }
 
     public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2) {
-        return new HashMap<K, V>() {{
+        return new HashMap<K, V>(2) {{
             put(k1, v1);
             put(k2, v2);
         }};
     }
 
     public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3) {
-        return new HashMap<K, V>() {{
+        return new HashMap<K, V>(3) {{
             put(k1, v1);
             put(k2, v2);
             put(k3, v3);
@@ -38,7 +38,7 @@ public final class HashMaps {
     }
 
     public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
-        return new HashMap<K, V>() {{
+        return new HashMap<K, V>(4) {{
             put(k1, v1);
             put(k2, v2);
             put(k3, v3);
@@ -47,7 +47,7 @@ public final class HashMaps {
     }
 
     public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
-        return new HashMap<K, V>() {{
+        return new HashMap<K, V>(5) {{
             put(k1, v1);
             put(k2, v2);
             put(k3, v3);
@@ -58,7 +58,7 @@ public final class HashMaps {
 
     public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
                                       K k6, V v6) {
-        return new HashMap<K, V>() {{
+        return new HashMap<K, V>(6) {{
             put(k1, v1);
             put(k2, v2);
             put(k3, v3);
@@ -70,7 +70,7 @@ public final class HashMaps {
 
     public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
                                       K k6, V v6, K k7, V v7) {
-        return new HashMap<K, V>() {{
+        return new HashMap<K, V>(7) {{
             put(k1, v1);
             put(k2, v2);
             put(k3, v3);
@@ -83,7 +83,7 @@ public final class HashMaps {
 
     public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
                                       K k6, V v6, K k7, V v7, K k8, V v8) {
-        return new HashMap<K, V>() {{
+        return new HashMap<K, V>(8) {{
             put(k1, v1);
             put(k2, v2);
             put(k3, v3);
@@ -97,7 +97,7 @@ public final class HashMaps {
 
     public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
                                       K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9) {
-        return new HashMap<K, V>() {{
+        return new HashMap<K, V>(9) {{
             put(k1, v1);
             put(k2, v2);
             put(k3, v3);
@@ -112,7 +112,7 @@ public final class HashMaps {
 
     public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5,
                                       K k6, V v6, K k7, V v7, K k8, V v8, K k9, V v9, K k10, V v10) {
-        return new HashMap<K, V>() {{
+        return new HashMap<K, V>(10) {{
             put(k1, v1);
             put(k2, v2);
             put(k3, v3);
@@ -145,12 +145,27 @@ public final class HashMaps {
     }
 
     @AllArgsConstructor
-    @Getter
-    @Setter
     @EqualsAndHashCode
     private static class SimpleEntry<K, V> implements Map.Entry<K, V> {
 
         private final K key;
         private V value;
+
+        @Override
+        public K getKey() {
+            return key;
+        }
+
+        @Override
+        public V getValue() {
+            return value;
+        }
+
+        @Override
+        public V setValue(V value) {
+            V prev = this.value;
+            this.value = value;
+            return prev;
+        }
     }
 }
diff --git a/src/test/java/ghast/HashMapsTest.java b/src/test/java/ghast/HashMapsTest.java
new file mode 100644
index 0000000..92d5e3e
--- /dev/null
+++ b/src/test/java/ghast/HashMapsTest.java
@@ -0,0 +1,182 @@
+package ghast;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class HashMapsTest {
+
+    @Test
+    void of0() {
+        Map<Object, Object> map = HashMaps.of();
+        assertNotNull(map);
+        assertTrue(map instanceof HashMap);
+        assertTrue(map.isEmpty());
+    }
+
+    @Test
+    void of1() {
+        Map<Object, Object> map = HashMaps.of("key1", "val1");
+        assertNotNull(map);
+        assertTrue(map instanceof HashMap);
+        assertEquals(1, map.size());
+    }
+
+    @Test
+    void of2() {
+        Map<Object, Object> map = HashMaps.of(
+                "key1", "val1",
+                "key2", "val2"
+        );
+        assertNotNull(map);
+        assertTrue(map instanceof HashMap);
+        assertEquals(2, map.size());
+    }
+
+    @Test
+    void of3() {
+        Map<Object, Object> map = HashMaps.of(
+                "key1", "val1",
+                "key2", "val2",
+                "key3", "val3"
+        );
+        assertNotNull(map);
+        assertTrue(map instanceof HashMap);
+        assertEquals(3, map.size());
+    }
+
+    @Test
+    void of4() {
+        Map<Object, Object> map = HashMaps.of(
+                "key1", "val1",
+                "key2", "val2",
+                "key3", "val3",
+                "key4", "val4"
+        );
+        assertNotNull(map);
+        assertTrue(map instanceof HashMap);
+        assertEquals(4, map.size());
+    }
+
+    @Test
+    void of5() {
+        Map<Object, Object> map = HashMaps.of(
+                "key1", "val1",
+                "key2", "val2",
+                "key3", "val3",
+                "key4", "val4",
+                "key5", "val5"
+        );
+        assertNotNull(map);
+        assertTrue(map instanceof HashMap);
+        assertEquals(5, map.size());
+    }
+
+    @Test
+    void of6() {
+        Map<Object, Object> map = HashMaps.of(
+                "key1", "val1",
+                "key2", "val2",
+                "key3", "val3",
+                "key4", "val4",
+                "key5", "val5",
+                "key6", "val6"
+        );
+        assertNotNull(map);
+        assertTrue(map instanceof HashMap);
+        assertEquals(6, map.size());
+    }
+
+    @Test
+    void of7() {
+        Map<Object, Object> map = HashMaps.of(
+                "key1", "val1",
+                "key2", "val2",
+                "key3", "val3",
+                "key4", "val4",
+                "key5", "val5",
+                "key6", "val6",
+                "key7", "val7"
+        );
+        assertNotNull(map);
+        assertTrue(map instanceof HashMap);
+        assertEquals(7, map.size());
+    }
+
+    @Test
+    void of8() {
+        Map<Object, Object> map = HashMaps.of(
+                "key1", "val1",
+                "key2", "val2",
+                "key3", "val3",
+                "key4", "val4",
+                "key5", "val5",
+                "key6", "val6",
+                "key7", "val7",
+                "key8", "val8"
+        );
+        assertNotNull(map);
+        assertTrue(map instanceof HashMap);
+        assertEquals(8, map.size());
+    }
+
+    @Test
+    void of9() {
+        Map<Object, Object> map = HashMaps.of(
+                "key1", "val1",
+                "key2", "val2",
+                "key3", "val3",
+                "key4", "val4",
+                "key5", "val5",
+                "key6", "val6",
+                "key7", "val7",
+                "key8", "val8",
+                "key9", "val9"
+        );
+        assertNotNull(map);
+        assertTrue(map instanceof HashMap);
+        assertEquals(9, map.size());
+    }
+
+    @Test
+    void of10() {
+        Map<Object, Object> map = HashMaps.of(
+                "key1", "val1",
+                "key2", "val2",
+                "key3", "val3",
+                "key4", "val4",
+                "key5", "val5",
+                "key6", "val6",
+                "key7", "val7",
+                "key8", "val8",
+                "key9", "val9",
+                "key10", "val10"
+        );
+        assertNotNull(map);
+        assertTrue(map instanceof HashMap);
+        assertEquals(10, map.size());
+    }
+
+    @Test
+    void ofEntries() {
+        Map<Object, Object> map = HashMaps.ofEntries(
+                HashMaps.entry("key1", "val1"),
+                HashMaps.entry("key2", "val2"),
+                HashMaps.entry("key3", "val3"),
+                HashMaps.entry("key4", "val4"),
+                HashMaps.entry("key5", "val5"),
+                HashMaps.entry("key6", "val6"),
+                HashMaps.entry("key7", "val7"),
+                HashMaps.entry("key8", "val8"),
+                HashMaps.entry("key9", "val9"),
+                HashMaps.entry("key10", "val10"),
+                HashMaps.entry("key11", "val11")
+        );
+        assertNotNull(map);
+        assertTrue(map instanceof HashMap);
+        assertEquals(11, map.size());
+    }
+}
\ No newline at end of file