diff --git a/src/DataMapper/DataMapper.php b/src/DataMapper/DataMapper.php
index 8424118a..5ce983b4 100644
--- a/src/DataMapper/DataMapper.php
+++ b/src/DataMapper/DataMapper.php
@@ -7,7 +7,6 @@
 use Mongolid\Connection\Connection;
 use Mongolid\Container\Container;
 use Mongolid\Cursor\CursorInterface;
-use Mongolid\Cursor\EagerLoadedCursor;
 use Mongolid\Cursor\SchemaCacheableCursor;
 use Mongolid\Cursor\SchemaCursor;
 use Mongolid\Event\EventTriggerService;
@@ -20,7 +19,7 @@
 /**
  * The DataMapper class will abstract how an Entity is persisted and retrieved
  * from the database.
- * The DataMapper will always use a Schema trough the SchemaMapper to parse the
+ * The DataMapper will always use a Schema through the SchemaMapper to parse the
  * document in and out of the database.
  */
 class DataMapper implements HasSchemaInterface
@@ -29,47 +28,35 @@ class DataMapper implements HasSchemaInterface
 
     /**
      * Name of the schema class to be used.
-     *
-     * @var string
      */
-    public $schemaClass = Schema::class;
+    public string $schemaClass = Schema::class;
 
     /**
      * Schema object. Will be set after the $schemaClass.
-     *
-     * @var Schema
-     */
-    protected $schema;
-
-    /**
-     * Connections that are going to be used to interact with the database.
-     *
-     * @var Connection
      */
-    protected $connection;
+    protected ?Schema $schema = null;
 
     /**
      * Have the responsibility of assembling the data coming from the database into actual entities.
-     *
-     * @var EntityAssembler
      */
-    protected $assembler;
+    protected ?EntityAssembler $assembler = null;
 
     /**
      * In order to dispatch events when necessary.
-     *
-     * @var EventTriggerService
      */
-    protected $eventService;
+    protected ?EventTriggerService $eventService = null;
 
     /**
-     * @var array
+     * @var array<string,null>
      */
-    private $pullNullValues = [];
+    private array $pullNullValues = [];
 
-    public function __construct(Connection $connection)
-    {
-        $this->connection = $connection;
+    public function __construct(
+        /**
+         * Connections that are going to be used to interact with the database.
+         */
+        protected Connection $connection
+    ) {
     }
 
     /**
@@ -83,7 +70,7 @@ public function __construct(Connection $connection)
      *
      * @return bool Success (but always false if write concern is Unacknowledged)
      */
-    public function save($entity, array $options = [])
+    public function save(mixed $entity, array $options = []): bool
     {
         // If the "saving" event returns false we'll bail out of the save and return
         // false, indicating that the save failed. This gives an opportunities to
@@ -125,7 +112,7 @@ public function save($entity, array $options = [])
      *
      * @return bool Success (but always false if write concern is Unacknowledged)
      */
-    public function insert($entity, array $options = [], bool $fireEvents = true): bool
+    public function insert(mixed $entity, array $options = [], bool $fireEvents = true): bool
     {
         if ($fireEvents && false === $this->fireEvent('inserting', $entity, true)) {
             return false;
@@ -163,7 +150,7 @@ public function insert($entity, array $options = [], bool $fireEvents = true): b
      *
      * @return bool Success (but always false if write concern is Unacknowledged)
      */
-    public function update($entity, array $options = []): bool
+    public function update(mixed $entity, array $options = []): bool
     {
         if (false === $this->fireEvent('updating', $entity, true)) {
             return false;
@@ -220,7 +207,7 @@ public function update($entity, array $options = []): bool
      *
      * @return bool Success (but always false if write concern is Unacknowledged)
      */
-    public function delete($entity, array $options = []): bool
+    public function delete(mixed $entity, array $options = []): bool
     {
         if (false === $this->fireEvent('deleting', $entity, true)) {
             return false;
@@ -253,7 +240,7 @@ public function delete($entity, array $options = []): bool
      * @param bool  $cacheable  retrieves a SchemaCacheableCursor instead
      */
     public function where(
-        $query = [],
+        mixed $query = [],
         array $projection = [],
         bool $cacheable = false
     ): CursorInterface {
@@ -301,10 +288,10 @@ public function all(): CursorInterface
      * @return mixed First document matching query as an $this->schema->entityClass object
      */
     public function first(
-        $query = [],
+        mixed $query = [],
         array $projection = [],
         bool $cacheable = false
-    ) {
+    ): mixed {
         if ($cacheable) {
             return $this->where($query, $projection, true)->first();
         }
@@ -322,12 +309,10 @@ public function first(
         );
 
         if (!$document) {
-            return;
+            return null;
         }
 
-        $model = $this->getAssembler()->assemble($document, $this->schema);
-
-        return $model;
+        return $this->getAssembler()->assemble($document, $this->schema);
     }
 
     /**
@@ -343,10 +328,10 @@ public function first(
      * @return mixed First document matching query as an $this->schema->entityClass object
      */
     public function firstOrFail(
-        $query = [],
+        mixed $query = [],
         array $projection = [],
         bool $cacheable = false
-    ) {
+    ): mixed {
         if ($result = $this->first($query, $projection, $cacheable)) {
             return $result;
         }
@@ -368,7 +353,7 @@ public function withoutSoftDelete(): self
      *
      * @return array Document
      */
-    protected function parseToDocument($entity)
+    protected function parseToDocument(mixed $entity): array
     {
         $schemaMapper = $this->getSchemaMapper();
         $parsedDocument = $schemaMapper->map($entity);
@@ -384,10 +369,8 @@ protected function parseToDocument($entity)
 
     /**
      * Returns a SchemaMapper with the $schema or $schemaClass instance.
-     *
-     * @return SchemaMapper
      */
-    protected function getSchemaMapper()
+    protected function getSchemaMapper(): SchemaMapper
     {
         if (!$this->schema) {
             $this->schema = Container::make($this->schemaClass);
@@ -407,20 +390,16 @@ public function getCollection(): Collection
             'typeMap' => ['array' => 'array', 'document' => 'array']
         ];
 
-        $collection = $this->connection
+        return $this->connection
             ->getClient()
             ->selectDatabase($database, $options)
             ->selectCollection($collectionName);
-
-        return $collection;
     }
 
     /**
      * Retrieves an EntityAssembler instance.
-     *
-     * @return EntityAssembler
      */
-    protected function getAssembler()
+    protected function getAssembler(): EntityAssembler
     {
         if (!$this->assembler) {
             $this->assembler = Container::make(EntityAssembler::class);
@@ -438,11 +417,13 @@ protected function getAssembler()
      *
      * @return mixed event handler return
      */
-    protected function fireEvent(string $event, $entity, bool $halt = false)
+    protected function fireEvent(string $event, mixed $entity, bool $halt = false): mixed
     {
-        $event = "mongolid.{$event}: ".get_class($entity);
+        $event = "mongolid.{$event}: ".$entity::class;
 
-        $this->eventService ? $this->eventService : $this->eventService = Container::make(EventTriggerService::class);
+        if (!$this->eventService) {
+            $this->eventService = Container::make(EventTriggerService::class);
+        }
 
         return $this->eventService->fire($event, $entity, $halt);
     }
@@ -468,9 +449,9 @@ protected function fireEvent(string $event, $entity, bool $halt = false)
      *
      * @throws InvalidArgumentException if the given $fields are not a valid projection
      *
-     * @return array
+     * @return array<string, bool>
      */
-    protected function prepareProjection(array $fields)
+    protected function prepareProjection(array $fields): array
     {
         $projection = [];
         foreach ($fields as $key => $value) {
@@ -489,7 +470,7 @@ protected function prepareProjection(array $fields)
 
             if (is_int($key) && is_string($value)) {
                 $key = $value;
-                if (0 === strpos($value, '-')) {
+                if (str_starts_with($value, '-')) {
                     $key = substr($key, 1);
                     $value = false;
                 } else {
@@ -518,20 +499,16 @@ protected function prepareProjection(array $fields)
      *
      * @param array $defaultOptions default options array
      * @param array $toMergeOptions to merge options array
-     *
-     * @return array
      */
-    private function mergeOptions(array $defaultOptions = [], array $toMergeOptions = [])
+    private function mergeOptions(array $defaultOptions = [], array $toMergeOptions = []): array
     {
         return array_merge($defaultOptions, $toMergeOptions);
     }
 
     /**
      * Perform actions on object before firing the after event.
-     *
-     * @param mixed $entity
      */
-    private function afterSuccess($entity)
+    private function afterSuccess(mixed $entity): void
     {
         if ($entity instanceof ModelInterface) {
             $entity->syncOriginalDocumentAttributes();
@@ -548,10 +525,8 @@ public function getSchema(): Schema
 
     /**
      * Set a Schema object  that describes an Entity in MongoDB.
-     *
-     * @param Schema $schema
      */
-    public function setSchema(Schema $schema)
+    public function setSchema(Schema $schema): void
     {
         $this->schema = $schema;
     }
@@ -580,7 +555,7 @@ private function getUpdateData($model, array $data): array
      * @see https://jira.mongodb.org/browse/SERVER-1014
      * @see https://github.com/bjori/mongo-php-transistor/blob/70f5af00795d67f4d5a8c397e831435814df9937/src/Transistor.php#L108
      */
-    private function calculateChanges(array &$changes, array $newData, array $oldData, string $keyfix = '')
+    private function calculateChanges(array &$changes, array $newData, array $oldData, string $keyfix = ''): void
     {
         foreach ($newData as $k => $v) {
             if (is_null($v)) {
@@ -610,22 +585,19 @@ private function calculateChanges(array &$changes, array $newData, array $oldDat
                     $this->pullNullValues[rtrim($keyfix, '.')] = null;
                 }
                 $changes['$unset']["{$keyfix}{$k}"] = '';
-                continue;
             }
         }
     }
 
     private function filterNullValues(array $data): array
     {
-        $filtered =  array_filter(
+        $filtered = array_filter(
             $data,
-            function ($value) {
-                return !is_null($value);
-            }
+            fn($value): bool => !is_null($value)
         );
 
         if ($data == array_values($data)) {
-            $filtered = array_values($filtered);
+            return array_values($filtered);
         }
 
         return $filtered;
diff --git a/src/DataMapper/EntityAssembler.php b/src/DataMapper/EntityAssembler.php
index 9f420c9b..647ffd0e 100644
--- a/src/DataMapper/EntityAssembler.php
+++ b/src/DataMapper/EntityAssembler.php
@@ -25,10 +25,8 @@ class EntityAssembler
      *
      * @param array|object $document the attributes that will be used to compose the entity
      * @param Schema       $schema   schema that will be used to map each field
-     *
-     * @return mixed
      */
-    public function assemble($document, Schema $schema)
+    public function assemble(array|object $document, Schema $schema): mixed
     {
         $entityClass = $schema->entityClass;
         $model = Container::make($entityClass);
@@ -36,7 +34,7 @@ public function assemble($document, Schema $schema)
         foreach ($document as $field => $value) {
             $fieldType = $schema->fields[$field] ?? null;
 
-            if ($fieldType && 'schema.' == substr($fieldType, 0, 7)) {
+            if ($fieldType && str_starts_with($fieldType, 'schema.')) {
                 $value = $this->assembleDocumentsRecursively($value, substr($fieldType, 7));
             }
 
@@ -58,12 +56,12 @@ public function assemble($document, Schema $schema)
      *
      * @return mixed the result of $entity->polymorph or the $entity itself
      */
-    protected function morphingTime(ModelInterface $entity)
+    protected function morphingTime(ModelInterface $entity): mixed
     {
         if ($entity instanceof PolymorphableModelInterface) {
             $class = $entity->polymorph($entity->getDocumentAttributes());
 
-            if ($class !== get_class($entity)) {
+            if ($class !== $entity::class) {
                 $originalAttributes = $entity->getDocumentAttributes();
                 $entity = Container::make($class);
                 $entity->fill($originalAttributes, true);
@@ -80,7 +78,7 @@ protected function morphingTime(ModelInterface $entity)
      *
      * @return mixed the entity with original attributes
      */
-    protected function prepareOriginalAttributes($entity)
+    protected function prepareOriginalAttributes(mixed $entity): mixed
     {
         if ($entity instanceof ModelInterface) {
             $entity->syncOriginalDocumentAttributes();
@@ -94,15 +92,13 @@ protected function prepareOriginalAttributes($entity)
      *
      * @param mixed  $value       a value of an embeded field containing entity data to be assembled
      * @param string $schemaClass the schemaClass to be used when assembling the entities within $value
-     *
-     * @return mixed
      */
-    protected function assembleDocumentsRecursively($value, string $schemaClass)
+    protected function assembleDocumentsRecursively(mixed $value, string $schemaClass): ?array
     {
         $value = (array) $value;
 
         if (empty($value)) {
-            return;
+            return null;
         }
 
         $schema = Container::make($schemaClass);
diff --git a/src/DataMapper/SchemaMapper.php b/src/DataMapper/SchemaMapper.php
index f77eb9fc..eb631aad 100644
--- a/src/DataMapper/SchemaMapper.php
+++ b/src/DataMapper/SchemaMapper.php
@@ -16,13 +16,6 @@
  */
 class SchemaMapper
 {
-    /**
-     * The actual schema to maps the data.
-     *
-     * @var Schema
-     */
-    public $schema;
-
     /**
      * Types that can be casted.
      *
@@ -30,14 +23,17 @@ class SchemaMapper
      *
      * @var string[]
      */
-    protected $castableTypes = ['int', 'integer', 'bool', 'boolean', 'float', 'double', 'real', 'string'];
+    protected array $castableTypes = ['int', 'integer', 'bool', 'boolean', 'float', 'double', 'real', 'string'];
 
     /**
      * @param Schema $schema schema that will be used to map each field
      */
-    public function __construct(Schema $schema)
-    {
-        $this->schema = $schema;
+    public function __construct(
+        /**
+         * The actual schema to maps the data.
+         */
+        public Schema $schema
+    ) {
     }
 
     /**
@@ -45,10 +41,8 @@ public function __construct(Schema $schema)
      *
      * @param array|object $data array or object with the fields that should
      *                           be mapped to $this->schema specifications
-     *
-     * @return array
      */
-    public function map($data)
+    public function map(array|object $data): array
     {
         $data = $this->parseToArray($data);
         $this->clearDynamic($data);
@@ -66,7 +60,7 @@ public function map($data)
      *
      * @param array $data Reference of the fields. The passed array will be modified.
      */
-    protected function clearDynamic(array &$data)
+    protected function clearDynamic(array &$data): void
     {
         if (!$this->schema->dynamic) {
             $data = array_intersect_key($data, $this->schema->fields);
@@ -74,20 +68,19 @@ protected function clearDynamic(array &$data)
     }
 
     /**
-     * Parse a value based on a field yype of the schema.
+     * Parse a value based on a field type of the schema.
      *
      * @param mixed  $value     value to be parsed
      * @param string $fieldType description of how the field should be treated
      *
      * @return mixed $value Value parsed to match $type
      */
-    public function parseField($value, string $fieldType)
+    public function parseField(mixed $value, string $fieldType): mixed
     {
         // Uses $fieldType method of the schema to parse the value
         if (method_exists($this->schema, $fieldType)) {
             return $this->schema->$fieldType($value);
         }
-
         // Returns null or an empty array
         if (null === $value || is_array($value) && empty($value)) {
             return $value;
@@ -99,7 +92,7 @@ public function parseField($value, string $fieldType)
         }
 
         // If the field type points to another schema.
-        if ('schema.' == substr($fieldType, 0, 7)) {
+        if (str_starts_with($fieldType, 'schema.')) {
             return $this->mapToSchema($value, substr($fieldType, 7));
         }
 
@@ -107,7 +100,7 @@ public function parseField($value, string $fieldType)
     }
 
     /**
-     * Uses PHP's settype to cast a value to a type.
+     * Uses PHP's set type to cast a value to a type.
      *
      * @see http://php.net/manual/pt_BR/function.settype.php
      *
@@ -116,7 +109,7 @@ public function parseField($value, string $fieldType)
      *
      * @return mixed
      */
-    protected function cast($value, string $type)
+    protected function cast(mixed $value, string $type): mixed
     {
         settype($value, $type);
 
@@ -129,10 +122,8 @@ protected function cast($value, string $type)
      *
      * @param mixed  $value       value that will be mapped
      * @param string $schemaClass class that will be passed to the new SchemaMapper constructor
-     *
-     * @return mixed
      */
-    protected function mapToSchema($value, string $schemaClass)
+    protected function mapToSchema(mixed $value, string $schemaClass): array
     {
         $value = (array) $value;
         $schema = Container::make($schemaClass);
@@ -153,17 +144,13 @@ protected function mapToSchema($value, string $schemaClass)
      * Parses an object to an array before sending it to the SchemaMapper.
      *
      * @param mixed $object the object that will be transformed into an array
-     *
-     * @return array
      */
-    protected function parseToArray($object): array
+    protected function parseToArray(mixed $object): array
     {
         if (!is_array($object)) {
-            $attributes = method_exists($object, 'getAttributes')
+            return method_exists($object, 'getAttributes')
                 ? $object->getAttributes()
                 : get_object_vars($object);
-
-            return $attributes;
         }
 
         return $object;
diff --git a/tests/Unit/DataMapper/DataMapperTest.php b/tests/Unit/DataMapper/DataMapperTest.php
index f388914f..379aa5a0 100644
--- a/tests/Unit/DataMapper/DataMapperTest.php
+++ b/tests/Unit/DataMapper/DataMapperTest.php
@@ -21,7 +21,7 @@
 
 class DataMapperTest extends TestCase
 {
-    protected m\MockInterface|EventTriggerService $eventService;
+    protected ?m\MockInterface $eventService = null;
 
     public function tearDown(): void
     {
@@ -33,7 +33,7 @@ public function tearDown(): void
     /**
      * @dataProvider getWriteConcernVariations
      */
-    public function testShouldSave($entity, $writeConcern, $shouldFireEventAfter, $expected)
+    public function testShouldSave(object $entity, int $writeConcern, bool $shouldFireEventAfter, bool $expected): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -94,7 +94,7 @@ public function testShouldSave($entity, $writeConcern, $shouldFireEventAfter, $e
     /**
      * @dataProvider getWriteConcernVariations
      */
-    public function testShouldInsert($entity, $writeConcern, $shouldFireEventAfter, $expected)
+    public function testShouldInsert(object $entity, int $writeConcern, bool $shouldFireEventAfter, bool $expected): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -152,7 +152,7 @@ public function testShouldInsert($entity, $writeConcern, $shouldFireEventAfter,
     /**
      * @dataProvider getWriteConcernVariations
      */
-    public function testShouldInsertWithoutFiringEvents($entity, $writeConcern, $shouldFireEventAfter, $expected)
+    public function testShouldInsertWithoutFiringEvents(object $entity, int $writeConcern, bool $shouldFireEventAfter, bool $expected): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -205,7 +205,7 @@ public function testShouldInsertWithoutFiringEvents($entity, $writeConcern, $sho
     /**
      * @dataProvider getWriteConcernVariations
      */
-    public function testShouldUpdate($entity, $writeConcern, $shouldFireEventAfter, $expected)
+    public function testShouldUpdate(object $entity, int $writeConcern, bool $shouldFireEventAfter, bool $expected): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -268,7 +268,7 @@ public function testShouldUpdate($entity, $writeConcern, $shouldFireEventAfter,
         $this->assertEquals($expected, $mapper->update($entity, $options));
     }
 
-    public function testDifferentialUpdateShouldWork()
+    public function testDifferentialUpdateShouldWork(): void
     {
         // Arrange
         $entity = m::mock(ModelInterface::class);
@@ -361,7 +361,7 @@ public function testDifferentialUpdateShouldWork()
         $this->assertTrue($mapper->update($entity, $options));
     }
 
-    public function testDifferentialUpdateShouldWorkHandlingNullValuesInArrays()
+    public function testDifferentialUpdateShouldWorkHandlingNullValuesInArrays(): void
     {
         // Arrange
         $entity = m::mock(ModelInterface::class);
@@ -476,7 +476,7 @@ public function testDifferentialUpdateShouldWorkHandlingNullValuesInArrays()
         $this->assertTrue($mapper->update($entity, $options));
     }
 
-    public function testDifferentialUpdateShouldReturnTrueIfThereIsNothingToUpdate()
+    public function testDifferentialUpdateShouldReturnTrueIfThereIsNothingToUpdate(): void
     {
         // Arrange
         $entity = m::mock(ModelInterface::class);
@@ -527,7 +527,7 @@ public function testUpdateShouldCallInsertWhenObjectHasNoId(
         $writeConcern,
         $shouldFireEventAfter,
         $expected
-    ) {
+    ): void {
         // Arrange
         $connection = m::mock(Connection::class);
         $mapper = m::mock(DataMapper::class.'[parseToDocument,getCollection]', [$connection]);
@@ -589,11 +589,11 @@ public function testUpdateShouldCallInsertWhenObjectHasNoId(
     /**
      * @dataProvider getWriteConcernVariations
      */
-    public function testShouldDelete($entity, $writeConcern, $shouldFireEventAfter, $expected)
+    public function testShouldDelete(object $entity, int $writeConcern, bool $shouldFireEventAfter, bool $expected): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
-        $mapper = m::mock(DataMapper::class.'[parseToDocument,getCollection]', [$connection]);
+        $mapper = m::mock(DataMapper::class . '[parseToDocument,getCollection]', [$connection]);
 
         $collection = m::mock(Collection::class);
         $parsedObject = ['_id' => 123];
@@ -621,7 +621,7 @@ public function testShouldDelete($entity, $writeConcern, $shouldFireEventAfter,
 
         $operationResult->shouldReceive('isAcknowledged')
             ->once()
-            ->andReturn((bool) $writeConcern);
+            ->andReturn((bool)$writeConcern);
 
         $operationResult->shouldReceive('getDeletedCount')
             ->andReturn(1);
@@ -648,13 +648,14 @@ public function testShouldDelete($entity, $writeConcern, $shouldFireEventAfter,
      * @dataProvider eventsToBailOperations
      */
     public function testDatabaseOperationsShouldBailOutIfTheEventHandlerReturnsFalse(
-        $operation,
-        $dbOperation,
-        $eventName
-    ) {
+        string $operation,
+        string $dbOperation,
+        string $eventName
+    ): void
+    {
         // Arrange
         $connection = m::mock(Connection::class);
-        $mapper = m::mock(DataMapper::class.'[parseToDocument,getCollection]', [$connection]);
+        $mapper = m::mock(DataMapper::class . '[parseToDocument,getCollection]', [$connection]);
         $collection = m::mock(Collection::class);
         $entity = m::mock();
 
@@ -681,7 +682,7 @@ public function testDatabaseOperationsShouldBailOutIfTheEventHandlerReturnsFalse
         $this->assertFalse($result);
     }
 
-    public function testShouldGetWithWhereQuery()
+    public function testShouldGetWithWhereQuery(): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -718,7 +719,7 @@ public function testShouldGetWithWhereQuery()
         $this->assertEquals($schema, $cacheableResult->entitySchema);
     }
 
-    public function testShouldGetAll()
+    public function testShouldGetAll(): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -738,7 +739,7 @@ public function testShouldGetAll()
         $this->assertEquals($mongolidCursor, $result);
     }
 
-    public function testShouldGetNullIfFirstCantFindAnything()
+    public function testShouldGetNullIfFirstCantFindAnything(): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -774,7 +775,7 @@ public function testShouldGetNullIfFirstCantFindAnything()
         $this->assertNull($result);
     }
 
-    public function testShouldGetFirstProjectingFields()
+    public function testShouldGetFirstProjectingFields(): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -813,7 +814,7 @@ public function testShouldGetFirstProjectingFields()
         $this->assertNull($result);
     }
 
-    public function testShouldGetFirstTroughACacheableCursor()
+    public function testShouldGetFirstTroughACacheableCursor(): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -839,7 +840,7 @@ public function testShouldGetFirstTroughACacheableCursor()
         $this->assertEquals($entity, $result);
     }
 
-    public function testShouldGetFirstTroughACacheableCursorProjectingFields()
+    public function testShouldGetFirstTroughACacheableCursorProjectingFields(): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -873,7 +874,7 @@ public function testShouldParseObjectToDocumentAndPutResultingIdIntoTheGivenObje
         $mapper = m::mock(DataMapper::class.'[getSchemaMapper]', [$connection]);
         $entity = m::mock();
         $parsedDocument = ['a_field' => 123, '_id' => 'bacon'];
-        $schemaMapper = m::mock(Schema::class.'[]');
+        $schemaMapper = m::mock(SchemaMapper::class.'[]');
 
         $mapper->shouldAllowMockingProtectedMethods();
 
@@ -898,7 +899,7 @@ public function testShouldParseObjectToDocumentAndPutResultingIdIntoTheGivenObje
         );
     }
 
-    public function testShouldGetSchemaMapper()
+    public function testShouldGetSchemaMapper(): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -916,7 +917,7 @@ public function testShouldGetSchemaMapper()
         $this->assertEquals($schema, $result->schema);
     }
 
-    public function testShouldGetRawCollection()
+    public function testShouldGetRawCollection(): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -952,7 +953,7 @@ public function testShouldGetRawCollection()
     /**
      * @dataProvider getProjections
      */
-    public function testPrepareProjectionShouldConvertArray($data, $expectation)
+    public function testPrepareProjectionShouldConvertArray(array $data, array $expectation): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -965,7 +966,7 @@ public function testPrepareProjectionShouldConvertArray($data, $expectation)
         $this->assertEquals($expectation, $result);
     }
 
-    public function testPrepareProjectionShouldThrownAnException()
+    public function testPrepareProjectionShouldThrownAnException(): void
     {
         // Arrange
         $connection = m::mock(Connection::class);
@@ -979,9 +980,9 @@ public function testPrepareProjectionShouldThrownAnException()
         $this->callProtected($mapper, 'prepareProjection', [$data]);
     }
 
-    protected function getEventService()
+    protected function getEventService(): m\MockInterface
     {
-        if (!($this->eventService ?? false)) {
+        if (!$this->eventService) {
             $this->eventService = m::mock(EventTriggerService::class);
             Container::instance(EventTriggerService::class, $this->eventService);
         }
@@ -989,7 +990,7 @@ protected function getEventService()
         return $this->eventService;
     }
 
-    protected function expectEventToBeFired($event, $entity, bool $halt, $return = true)
+    protected function expectEventToBeFired(string $event, object $entity, bool $halt, bool $return = true): void
     {
         $event = 'mongolid.'.$event.': '.get_class($entity);
 
@@ -1000,7 +1001,7 @@ protected function expectEventToBeFired($event, $entity, bool $halt, $return = t
             ->andReturn($return);
     }
 
-    protected function expectEventNotToBeFired($event, $entity)
+    protected function expectEventNotToBeFired(string $event, object $entity): void
     {
         $event = 'mongolid.'.$event.': '.get_class($entity);
 
@@ -1009,7 +1010,7 @@ protected function expectEventNotToBeFired($event, $entity)
             ->never();
     }
 
-    public function eventsToBailOperations()
+    public function eventsToBailOperations(): array
     {
         return [
             'Saving event' => [
@@ -1038,7 +1039,7 @@ public function eventsToBailOperations()
         ];
     }
 
-    public function getWriteConcernVariations()
+    public function getWriteConcernVariations(): array
     {
         return [
             'acknowledged write concern with plain object' => [
@@ -1071,7 +1072,7 @@ public function getWriteConcernVariations()
     /**
      * Retrieves projections that should be replaced by mapper.
      */
-    public function getProjections()
+    public function getProjections(): array
     {
         return [
             'Should return self array' => [
diff --git a/tests/Unit/DataMapper/SchemaMapperTest.php b/tests/Unit/DataMapper/SchemaMapperTest.php
index 95e731ab..e5dae598 100644
--- a/tests/Unit/DataMapper/SchemaMapperTest.php
+++ b/tests/Unit/DataMapper/SchemaMapperTest.php
@@ -15,7 +15,7 @@ public function tearDown(): void
         m::close();
     }
 
-    public function testShouldMapToFieldsOfSchema()
+    public function testShouldMapToFieldsOfSchema(): void
     {
         // Arrange
         $schema = m::mock(Schema::class);
@@ -58,7 +58,7 @@ public function testShouldMapToFieldsOfSchema()
         );
     }
 
-    public function testShouldClearDynamicFieldsIfSchemaIsNotDynamic()
+    public function testShouldClearDynamicFieldsIfSchemaIsNotDynamic(): void
     {
         // Arrange
         $schema = m::mock(Schema::class);
@@ -85,7 +85,7 @@ public function testShouldClearDynamicFieldsIfSchemaIsNotDynamic()
         );
     }
 
-    public function testShouldNotClearDynamicFieldsIfSchemaIsDynamic()
+    public function testShouldNotClearDynamicFieldsIfSchemaIsDynamic(): void
     {
         // Arrange
         $schema = m::mock(Schema::class);
@@ -113,7 +113,7 @@ public function testShouldNotClearDynamicFieldsIfSchemaIsDynamic()
         );
     }
 
-    public function testShouldParseFieldIntoCastableType()
+    public function testShouldParseFieldIntoCastableType(): void
     {
         // Arrange
         $schema = m::mock(Schema::class);
@@ -131,7 +131,7 @@ public function testShouldParseFieldIntoCastableType()
         );
     }
 
-    public function testShouldParseFieldIntoAnotherMappedSchemaIfTypeBeginsWithSchema()
+    public function testShouldParseFieldIntoAnotherMappedSchemaIfTypeBeginsWithSchema(): void
     {
         // Arrange
         $schema = m::mock(Schema::class);
@@ -154,7 +154,7 @@ public function testShouldParseFieldIntoAnotherMappedSchemaIfTypeBeginsWithSchem
         );
     }
 
-    public function testShouldParseFieldUsingAMethodInSchemaIfTypeIsAnUnknownString()
+    public function testShouldParseFieldUsingAMethodInSchemaIfTypeIsAnUnknownString(): void
     {
         // Arrange
         $schemaClass = new class() extends Schema {
@@ -174,7 +174,7 @@ public function pumpkinPoint($value)
         );
     }
 
-    public function testShouldMapAnArrayValueToAnotherSchema()
+    public function testShouldMapAnArrayValueToAnotherSchema(): void
     {
         // Arrange
         $schema = m::mock(Schema::class);
@@ -187,7 +187,7 @@ public function testShouldMapAnArrayValueToAnotherSchema()
         Container::instance('Xd\MySchema', $mySchema);
 
         // When instantiating the SchemaMapper with the specified $param as dependency
-        Container::bind(SchemaMapper::class, function ($container, $params) use ($value, $mySchema, $test) {
+        Container::bind(SchemaMapper::class, function ($container, $params) use ($value, $mySchema, $test): \Mockery\LegacyMockInterface {
             // Check if mySchema has been injected correctly
             $test->assertSame($mySchema, $params['schema']);
 
@@ -212,7 +212,7 @@ public function testShouldMapAnArrayValueToAnotherSchema()
         );
     }
 
-    public function testShouldParseToArrayGettingObjectAttributes()
+    public function testShouldParseToArrayGettingObjectAttributes(): void
     {
         // Arrange
         $schema = m::mock(Schema::class);
@@ -226,7 +226,7 @@ public function testShouldParseToArrayGettingObjectAttributes()
         );
     }
 
-    public function testShouldParseToArrayIfIsAnArray()
+    public function testShouldParseToArrayIfIsAnArray(): void
     {
         // Arrange
         $schema = m::mock(Schema::class);
@@ -240,13 +240,16 @@ public function testShouldParseToArrayIfIsAnArray()
         );
     }
 
-    public function testShouldGetAttributesWhenGetAttributesMethodIsAvailable()
+    public function testShouldGetAttributesWhenGetAttributesMethodIsAvailable(): void
     {
         // Arrange
         $schema = m::mock(Schema::class);
         $schemaMapper = new SchemaMapper($schema);
         $object = new class() {
-            public function getAttributes()
+            /**
+             * @return array{foo: string}
+             */
+            public function getAttributes(): array
             {
                 return ['foo' => 'bar'];
             }