diff --git a/tests/framework/db/ExpressionTest.php b/tests/framework/db/ExpressionTest.php
new file mode 100644
index 00000000000..57bb5d6caf3
--- /dev/null
+++ b/tests/framework/db/ExpressionTest.php
@@ -0,0 +1,89 @@
+<?php
+
+/**
+ * @link https://www.yiiframework.com/
+ * @copyright Copyright (c) 2008 Yii Software LLC
+ * @license https://www.yiiframework.com/license/
+ */
+
+declare(strict_types=1);
+
+namespace yiiunit\framework\db;
+
+use yii\db\Expression;
+use yii\db\ExpressionInterface;
+use yiiunit\TestCase;
+
+/**
+ * @group db
+ */
+class ExpressionTest extends TestCase
+{
+    public function testConstructor(): void
+    {
+        $expression = new Expression('NOW()');
+
+        self::assertSame('NOW()', $expression->expression);
+        self::assertSame([], $expression->params);
+    }
+
+    public function testConstructorWithConfig(): void
+    {
+        $expression = new Expression('DEFAULT', [], ['expression' => 'overridden']);
+
+        self::assertSame('overridden', $expression->expression);
+    }
+
+    public function testToString(): void
+    {
+        $expression = new Expression('COUNT(*)');
+
+        self::assertSame('COUNT(*)', (string) $expression);
+        self::assertSame('COUNT(*)', $expression->__toString());
+    }
+
+    public function testImplementsExpressionInterface(): void
+    {
+        $expression = new Expression('1');
+
+        self::assertInstanceOf(ExpressionInterface::class, $expression);
+    }
+
+    public function testEmptyExpression(): void
+    {
+        $expression = new Expression('');
+
+        self::assertSame('', $expression->expression);
+        self::assertSame('', (string) $expression);
+    }
+
+    /**
+     * @dataProvider expressionsProvider
+     */
+    public function testVariousExpressions(string $sql, array $params): void
+    {
+        $expression = new Expression($sql, $params);
+
+        self::assertSame($sql, (string) $expression);
+        self::assertSame($params, $expression->params);
+    }
+
+    public static function expressionsProvider(): array
+    {
+        return [
+            'simple function' => ['NOW()', []],
+            'aggregate' => ['COUNT(*)', []],
+            'with placeholder' => ['status = :status', [':status' => 1]],
+            'multiple placeholders' => [
+                'age BETWEEN :min AND :max',
+                [':min' => 18, ':max' => 65],
+            ],
+            'subquery-like' => ['(SELECT MAX(id) FROM users)', []],
+            'raw literal' => ['1', []],
+            'complex expression' => [
+                'CASE WHEN status = :active THEN 1 ELSE 0 END',
+                [':active' => 'active'],
+            ],
+        ];
+    }
+}
diff --git a/tests/framework/db/JsonExpressionTest.php b/tests/framework/db/JsonExpressionTest.php
new file mode 100644
index 00000000000..0d47c4346b5
--- /dev/null
+++ b/tests/framework/db/JsonExpressionTest.php
@@ -0,0 +1,151 @@
+<?php
+
+/**
+ * @link https://www.yiiframework.com/
+ * @copyright Copyright (c) 2008 Yii Software LLC
+ * @license https://www.yiiframework.com/license/
+ */
+
+declare(strict_types=1);
+
+namespace yiiunit\framework\db;
+
+use yii\base\InvalidConfigException;
+use yii\db\ExpressionInterface;
+use yii\db\JsonExpression;
+use yii\db\Query;
+use yiiunit\TestCase;
+
+/**
+ * @group db
+ */
+class JsonExpressionTest extends TestCase
+{
+    public function testConstructorWithArray(): void
+    {
+        $data = ['a' => 1, 'b' => 2];
+        $expression = new JsonExpression($data);
+
+        self::assertSame($data, $expression->getValue());
+        self::assertNull($expression->getType());
+    }
+
+    public function testConstructorWithType(): void
+    {
+        $expression = new JsonExpression([1, 2, 3], JsonExpression::TYPE_JSON);
+
+        self::assertSame(JsonExpression::TYPE_JSON, $expression->getType());
+    }
+
+    public function testConstructorWithJsonbType(): void
+    {
+        $expression = new JsonExpression(['key' => 'val'], JsonExpression::TYPE_JSONB);
+
+        self::assertSame(JsonExpression::TYPE_JSONB, $expression->getType());
+    }
+
+    public function testUnwrapsNestedJsonExpression(): void
+    {
+        $inner = new JsonExpression(['nested' => true]);
+        $outer = new JsonExpression($inner);
+
+        self::assertSame(['nested' => true], $outer->getValue());
+    }
+
+    public function testUnwrapsNestedJsonExpressionPreservesOuterType(): void
+    {
+        $inner = new JsonExpression(['data' => 1], JsonExpression::TYPE_JSON);
+        $outer = new JsonExpression($inner, JsonExpression::TYPE_JSONB);
+
+        self::assertSame(['data' => 1], $outer->getValue());
+        self::assertSame(JsonExpression::TYPE_JSONB, $outer->getType());
+    }
+
+    public function testUnwrapsOnlyOneLevel(): void
+    {
+        $innermost = new JsonExpression('deep');
+        $middle = new JsonExpression($innermost);
+        $outer = new JsonExpression($middle);
+
+        self::assertSame('deep', $outer->getValue());
+    }
+
+    public function testImplementsExpressionInterface(): void
+    {
+        $expression = new JsonExpression([]);
+
+        self::assertInstanceOf(ExpressionInterface::class, $expression);
+    }
+
+    public function testImplementsJsonSerializable(): void
+    {
+        $expression = new JsonExpression([]);
+
+        self::assertInstanceOf(\JsonSerializable::class, $expression);
+    }
+
+    public function testJsonSerializeReturnsValue(): void
+    {
+        $data = ['x' => 10, 'y' => 20];
+        $expression = new JsonExpression($data);
+
+        self::assertSame($data, $expression->jsonSerialize());
+    }
+
+    public function testJsonSerializeWithScalar(): void
+    {
+        $expression = new JsonExpression('string value');
+
+        self::assertSame('string value', $expression->jsonSerialize());
+    }
+
+    public function testJsonSerializeWithNull(): void
+    {
+        $expression = new JsonExpression(null);
+
+        self::assertNull($expression->jsonSerialize());
+    }
+
+    public function testJsonSerializeThrowsOnQueryInterface(): void
+    {
+        $query = new Query();
+        $expression = new JsonExpression($query);
+
+        $this->expectException(InvalidConfigException::class);
+        $expression->jsonSerialize();
+    }
+
+    public function testJsonEncodeUsesJsonSerialize(): void
+    {
+        $data = ['name' => 'test', 'count' => 42];
+        $expression = new JsonExpression($data);
+
+        self::assertSame('{"name":"test","count":42}', json_encode($expression));
+    }
+
+    /**
+     * @dataProvider valueTypesProvider
+     */
+    public function testAcceptsVariousValueTypes($value): void
+    {
+        $expression = new JsonExpression($value);
+
+        self::assertSame($value, $expression->getValue());
+    }
+
+    public static function valueTypesProvider(): array
+    {
+        return [
+            'array' => [['a', 'b', 'c']],
+            'associative array' => [['key' => 'value']],
+            'nested array' => [['a' => ['b' => ['c' => 1]]]],
+            'string' => ['simple string'],
+            'integer' => [42],
+            'float' => [3.14],
+            'boolean true' => [true],
+            'boolean false' => [false],
+            'null' => [null],
+            'empty array' => [[]],
+        ];
+    }
+}
diff --git a/tests/framework/db/TableSchemaTest.php b/tests/framework/db/TableSchemaTest.php
new file mode 100644
index 00000000000..f1a28138932
--- /dev/null
+++ b/tests/framework/db/TableSchemaTest.php
@@ -0,0 +1,141 @@
+<?php
+
+/**
+ * @link https://www.yiiframework.com/
+ * @copyright Copyright (c) 2008 Yii Software LLC
+ * @license https://www.yiiframework.com/license/
+ */
+
+declare(strict_types=1);
+
+namespace yiiunit\framework\db;
+
+use yii\base\InvalidArgumentException;
+use yii\db\ColumnSchema;
+use yii\db\TableSchema;
+use yiiunit\TestCase;
+
+/**
+ * @group db
+ */
+class TableSchemaTest extends TestCase
+{
+    private function createTableSchema(array $columnNames = ['id', 'name', 'email']): TableSchema
+    {
+        $table = new TableSchema();
+        $table->name = 'test_table';
+        $table->fullName = 'test_table';
+
+        foreach ($columnNames as $name) {
+            $column = new ColumnSchema();
+            $column->name = $name;
+            $column->isPrimaryKey = false;
+            $table->columns[$name] = $column;
+        }
+
+        return $table;
+    }
+
+    public function testGetColumnReturnsColumnSchema(): void
+    {
+        $table = $this->createTableSchema();
+
+        $column = $table->getColumn('name');
+
+        self::assertInstanceOf(ColumnSchema::class, $column);
+        self::assertSame('name', $column->name);
+    }
+
+    public function testGetColumnReturnsNullForNonExistent(): void
+    {
+        $table = $this->createTableSchema();
+
+        self::assertNull($table->getColumn('nonexistent'));
+    }
+
+    public function testGetColumnNames(): void
+    {
+        $table = $this->createTableSchema(['id', 'name', 'email']);
+
+        self::assertSame(['id', 'name', 'email'], $table->getColumnNames());
+    }
+
+    public function testGetColumnNamesEmpty(): void
+    {
+        $table = $this->createTableSchema([]);
+
+        self::assertSame([], $table->getColumnNames());
+    }
+
+    public function testColumnNamesProperty(): void
+    {
+        $table = $this->createTableSchema(['a', 'b']);
+
+        self::assertSame(['a', 'b'], $table->columnNames);
+    }
+
+    public function testFixPrimaryKeyWithSingleKey(): void
+    {
+        $table = $this->createTableSchema();
+
+        $table->fixPrimaryKey('id');
+
+        self::assertSame(['id'], $table->primaryKey);
+        self::assertTrue($table->columns['id']->isPrimaryKey);
+        self::assertFalse($table->columns['name']->isPrimaryKey);
+        self::assertFalse($table->columns['email']->isPrimaryKey);
+    }
+
+    public function testFixPrimaryKeyWithCompositeKey(): void
+    {
+        $table = $this->createTableSchema(['user_id', 'role_id', 'data']);
+
+        $table->fixPrimaryKey(['user_id', 'role_id']);
+
+        self::assertSame(['user_id', 'role_id'], $table->primaryKey);
+        self::assertTrue($table->columns['user_id']->isPrimaryKey);
+        self::assertTrue($table->columns['role_id']->isPrimaryKey);
+        self::assertFalse($table->columns['data']->isPrimaryKey);
+    }
+
+    public function testFixPrimaryKeyResetsOldPrimaryKey(): void
+    {
+        $table = $this->createTableSchema();
+        $table->columns['id']->isPrimaryKey = true;
+        $table->primaryKey = ['id'];
+
+        $table->fixPrimaryKey('name');
+
+        self::assertSame(['name'], $table->primaryKey);
+        self::assertFalse($table->columns['id']->isPrimaryKey);
+        self::assertTrue($table->columns['name']->isPrimaryKey);
+    }
+
+    public function testFixPrimaryKeyThrowsOnNonExistentColumn(): void
+    {
+        $table = $this->createTableSchema();
+
+        $this->expectException(InvalidArgumentException::class);
+        $table->fixPrimaryKey('nonexistent');
+    }
+
+    public function testFixPrimaryKeyThrowsOnPartialComposite(): void
+    {
+        $table = $this->createTableSchema();
+
+        $this->expectException(InvalidArgumentException::class);
+        $table->fixPrimaryKey(['id', 'missing']);
+    }
+
+    public function testFixPrimaryKeyWithEmptyArray(): void
+    {
+        $table = $this->createTableSchema();
+        $table->columns['id']->isPrimaryKey = true;
+        $table->primaryKey = ['id'];
+
+        $table->fixPrimaryKey([]);
+
+        self::assertSame([], $table->primaryKey);
+        self::assertFalse($table->columns['id']->isPrimaryKey);
+    }
+}