Use countDocument or estimatedDocumentsCount when no filter is provided

Add functional test

Author: GromNaN

src/Query/Builder.php

@@ -273,7 +273,11 @@ public function toMql(): array
                     $aggregations = blank($this->aggregate['columns']) ? [] : $this->aggregate['columns'];
 
                     if (in_array('*', $aggregations) && $function == 'count') {
-                        return ['estimatedDocumentCount' => [$wheres, []]];
+                        if ($wheres) {
+                            return ['countDocuments' => [$wheres, []]];
+                        }
+
+                        return ['estimatedDocumentCount' => [[], []]];
                     } elseif ($function == 'count') {
                         // Translate count into sum.
                         $group['aggregate'] = ['$sum' => 1];

tests/TransactionTest.php

@@ -291,6 +291,32 @@ public function testDecrementWithRollBack(): void
         $this->assertTrue(DB::collection('users')->where('name', 'klinson')->where('age', 20)->exists());
     }
 
+    /**
+     * @testWith [false]
+     *           [true]
+     */
+    public function testCount(bool $transaction)
+    {
+        if ($transaction) {
+            DB::beginTransaction();
+        }
+
+        $this->assertEquals(0, DB::collection('users')->count());
+        $this->assertEquals(0, DB::collection('users')->where('age', 20)->count());
+        DB::collection('users')->insert(['name' => 'klinson', 'age' => 20, 'title' => 'admin']);
+        DB::collection('users')->insert(['name' => 'bryan', 'age' => 18, 'title' => 'user']);
+        $this->assertEquals(2, DB::collection('users')->count());
+
+        if ($transaction) {
+            // until transaction is committed, count with filter is incorrect
+            $this->assertEquals(0, DB::collection('users')->where('age', 20)->count());
+            DB::commit();
+        }
+
+        $this->assertEquals(1, DB::collection('users')->where('age', 20)->count());
+        $this->assertEquals(0, DB::collection('users')->where('age', 10)->count());
+    }
+
     public function testQuery()
     {
         /** rollback test */