diff --git a/tests/e2e/auth-flow.test.ts b/tests/e2e/auth-flow.test.ts
index 64b7fdc..99d1804 100644
--- a/tests/e2e/auth-flow.test.ts
+++ b/tests/e2e/auth-flow.test.ts
@@ -85,8 +85,10 @@ test.describe('Authentication Flow', () => {
       const errorMessage = page.locator('.error, [role="alert"], .text-red')
       const hasError = await errorMessage.count()
 
-      // Either error shown or still on login page
-      expect(hasError >= 0).toBe(true)
+      // Verify login was rejected: either error shown or still on login page
+      const loginDialog = page.locator('[data-testid="login-dialog"]')
+      const isStillOnLoginPage = await loginDialog.isVisible().catch(() => false)
+      expect(hasError > 0 || isStillOnLoginPage).toBe(true)
     }
   })
 })
diff --git a/tests/unit/mysql.test.ts b/tests/unit/mysql.test.ts
index 3a4c72f..70afb99 100644
--- a/tests/unit/mysql.test.ts
+++ b/tests/unit/mysql.test.ts
@@ -1,11 +1,51 @@
 /**
  * Unit tests for MySqlService
- * These tests do not require a MySQL instance
+ * Covers both unconnected state and connected-path operations using mocked mysql2/promise.
  */
 
-import { describe, it, expect, beforeEach } from 'vitest'
+import { describe, it, expect, beforeEach, vi } from 'vitest'
 import { MySqlService } from '@services/database/mysql'
 
+// ---- Hoisted mock functions ----
+const {
+  mockCreateConnection,
+  mockPing,
+  mockExecute,
+  mockBeginTransaction,
+  mockCommit,
+  mockRollback,
+  mockEnd
+} = vi.hoisted(() => ({
+  mockCreateConnection: vi.fn(),
+  mockPing: vi.fn(),
+  mockExecute: vi.fn(),
+  mockBeginTransaction: vi.fn(),
+  mockCommit: vi.fn(),
+  mockRollback: vi.fn(),
+  mockEnd: vi.fn()
+}))
+
+// Mock mysql2/promise driver
+vi.mock('mysql2/promise', () => ({
+  default: {
+    createConnection: mockCreateConnection
+  }
+}))
+
+// Mock logger
+vi.mock('@services/logger', () => ({
+  createLogger: () => ({
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+    debug: vi.fn()
+  }),
+  trackDuration: async <T>(fn: () => Promise<T>) => {
+    const result = await fn()
+    return { result }
+  }
+}))
+
 const mockConfig = {
   host: 'localhost',
   port: 3306,
@@ -14,11 +54,30 @@ const mockConfig = {
   database: 'testdb'
 }
 
+function createMockConnection() {
+  return {
+    ping: mockPing,
+    execute: mockExecute,
+    beginTransaction: mockBeginTransaction,
+    commit: mockCommit,
+    rollback: mockRollback,
+    end: mockEnd
+  }
+}
+
 describe('MySqlService Unit Tests', () => {
   let service: MySqlService
 
   beforeEach(() => {
+    vi.clearAllMocks()
     service = new MySqlService(mockConfig)
+    mockCreateConnection.mockResolvedValue(createMockConnection())
+    mockPing.mockResolvedValue(undefined)
+    mockExecute.mockResolvedValue([[], []])
+    mockBeginTransaction.mockResolvedValue(undefined)
+    mockCommit.mockResolvedValue(undefined)
+    mockRollback.mockResolvedValue(undefined)
+    mockEnd.mockResolvedValue(undefined)
   })
 
   describe('constructor', () => {
@@ -35,15 +94,33 @@ describe('MySqlService Unit Tests', () => {
   })
 
   describe('connect', () => {
-    it('should throw error with invalid credentials', async () => {
-      // This tests error handling without needing a real server
-      const invalidConfig = {
-        ...mockConfig,
-        host: 'invalid-host-that-does-not-exist'
-      }
-      const invalidService = new MySqlService(invalidConfig)
+    it('should throw error when connection fails', async () => {
+      mockCreateConnection.mockRejectedValue(new Error('connect ECONNREFUSED'))
+      await expect(service.connect()).rejects.toThrow('Failed to connect to MySQL')
+    })
 
-      await expect(invalidService.connect()).rejects.toThrow('Failed to connect to MySQL')
+    it('should establish connection and ping server', async () => {
+      await service.connect()
+      expect(mockCreateConnection).toHaveBeenCalledWith({
+        host: 'localhost',
+        port: 3306,
+        user: 'test',
+        password: 'test',
+        database: 'testdb'
+      })
+      expect(mockPing).toHaveBeenCalled()
+      expect(service.isConnected()).toBe(true)
+    })
+
+    it('should throw when already connected', async () => {
+      await service.connect()
+      await expect(service.connect()).rejects.toThrow('Already connected to MySQL')
+    })
+
+    it('should throw when ping fails after connection created', async () => {
+      mockPing.mockRejectedValue(new Error('ping failed'))
+      await expect(service.connect()).rejects.toThrow('Failed to connect to MySQL')
+      // Note: source sets connection before ping, so it remains non-null after ping failure
     })
   })
 
@@ -51,6 +128,51 @@ describe('MySqlService Unit Tests', () => {
     it('should throw error when not connected', async () => {
       await expect(service.query('SELECT 1')).rejects.toThrow('Not connected to MySQL')
     })
+
+    it('should execute SELECT and return rows with columns', async () => {
+      await service.connect()
+      mockExecute.mockResolvedValue([
+        [{ id: 1, name: 'test' }, { id: 2, name: 'foo' }],
+        [{ name: 'id' }, { name: 'name' }]
+      ])
+
+      const result = await service.query('SELECT id, name FROM users')
+
+      expect(mockExecute).toHaveBeenCalledWith('SELECT id, name FROM users', undefined)
+      expect(result.rows).toEqual([
+        { id: 1, name: 'test' },
+        { id: 2, name: 'foo' }
+      ])
+      expect(result.columns).toEqual(['id', 'name'])
+      expect(result.rowCount).toBe(2)
+    })
+
+    it('should execute INSERT/UPDATE and return affected rows', async () => {
+      await service.connect()
+      mockExecute.mockResolvedValue([{ affectedRows: 3, changedRows: 2 }, []])
+
+      const result = await service.query('UPDATE users SET active = ?', [true])
+
+      expect(mockExecute).toHaveBeenCalledWith('UPDATE users SET active = ?', [true])
+      expect(result.rows).toEqual([])
+      expect(result.rowCount).toBe(3)
+    })
+
+    it('should use changedRows when affectedRows is zero', async () => {
+      await service.connect()
+      mockExecute.mockResolvedValue([{ affectedRows: 0, changedRows: 5 }, []])
+
+      const result = await service.query('UPDATE users SET x = 1')
+
+      expect(result.rowCount).toBe(5)
+    })
+
+    it('should wrap query errors with context', async () => {
+      await service.connect()
+      mockExecute.mockRejectedValue(new Error('syntax error'))
+
+      await expect(service.query('INVALID SQL')).rejects.toThrow('MySQL query failed')
+    })
   })
 
   describe('transaction', () => {
@@ -59,11 +181,56 @@ describe('MySqlService Unit Tests', () => {
         'Not connected to MySQL'
       )
     })
+
+    it('should execute all queries and commit', async () => {
+      await service.connect()
+
+      await service.transaction([
+        { sql: 'INSERT INTO t VALUES (?)', params: [1] },
+        { sql: 'UPDATE t SET x = ?' }
+      ])
+
+      expect(mockBeginTransaction).toHaveBeenCalled()
+      expect(mockExecute).toHaveBeenCalledTimes(2)
+      expect(mockExecute).toHaveBeenNthCalledWith(1, 'INSERT INTO t VALUES (?)', [1])
+      expect(mockExecute).toHaveBeenNthCalledWith(2, 'UPDATE t SET x = ?', undefined)
+      expect(mockCommit).toHaveBeenCalled()
+      expect(mockRollback).not.toHaveBeenCalled()
+    })
+
+    it('should rollback on query failure', async () => {
+      await service.connect()
+      mockExecute.mockRejectedValueOnce(new Error('constraint violation'))
+
+      await expect(
+        service.transaction([{ sql: 'INSERT INTO t VALUES (?)', params: [1] }])
+      ).rejects.toThrow('MySQL transaction failed')
+
+      expect(mockRollback).toHaveBeenCalled()
+      expect(mockCommit).not.toHaveBeenCalled()
+    })
   })
 
   describe('disconnect', () => {
     it('should resolve when not connected', async () => {
       await expect(service.disconnect()).resolves.not.toThrow()
     })
+
+    it('should end connection and reset state', async () => {
+      await service.connect()
+      expect(service.isConnected()).toBe(true)
+
+      await service.disconnect()
+
+      expect(mockEnd).toHaveBeenCalled()
+      expect(service.isConnected()).toBe(false)
+    })
+
+    it('should wrap disconnect errors', async () => {
+      await service.connect()
+      mockEnd.mockRejectedValue(new Error('connection lost'))
+
+      await expect(service.disconnect()).rejects.toThrow('Failed to disconnect from MySQL')
+    })
   })
 })
diff --git a/tests/unit/postgresql.test.ts b/tests/unit/postgresql.test.ts
index 647a9e7..78ec25e 100644
--- a/tests/unit/postgresql.test.ts
+++ b/tests/unit/postgresql.test.ts
@@ -1,11 +1,47 @@
 /**
  * Unit tests for PostgreSqlService
- * These tests do not require a PostgreSQL instance
+ * Covers both unconnected state and connected-path operations using mocked pg driver.
+ * Also tests the prepareSql pure function (no mocks needed for those).
  */
 
-import { describe, it, expect, beforeEach } from 'vitest'
+import { describe, it, expect, beforeEach, vi } from 'vitest'
 import { PostgreSqlService, prepareSql } from '@main/services/database/postgresql'
 
+// ---- Hoisted mock functions ----
+const { mockPgPool, mockPgClient } = vi.hoisted(() => {
+  const client = {
+    query: vi.fn(),
+    release: vi.fn()
+  }
+  const pool = {
+    connect: vi.fn(() => client),
+    query: vi.fn(),
+    end: vi.fn()
+  }
+  return { mockPgPool: pool, mockPgClient: client }
+})
+
+// Mock pg driver (must use regular function because source uses `new Pool(...)`)
+vi.mock('pg', () => ({
+  Pool: vi.fn(function () {
+    return mockPgPool
+  })
+}))
+
+// Mock logger
+vi.mock('@main/services/logger', () => ({
+  createLogger: () => ({
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+    debug: vi.fn()
+  }),
+  trackDuration: async <T>(fn: () => Promise<T>) => {
+    const result = await fn()
+    return { result }
+  }
+}))
+
 const mockConfig = {
   host: 'localhost',
   port: 5432,
@@ -18,7 +54,13 @@ describe('PostgreSqlService Unit Tests', () => {
   let service: PostgreSqlService
 
   beforeEach(() => {
+    vi.clearAllMocks()
     service = new PostgreSqlService(mockConfig)
+    mockPgPool.connect.mockResolvedValue(mockPgClient)
+    mockPgPool.query.mockResolvedValue({ rows: [], fields: [], rowCount: 0 })
+    mockPgPool.end.mockResolvedValue(undefined)
+    mockPgClient.query.mockResolvedValue({ rows: [] })
+    mockPgClient.release.mockReturnValue(undefined)
   })
 
   describe('constructor', () => {
@@ -40,10 +82,79 @@ describe('PostgreSqlService Unit Tests', () => {
     })
   })
 
+  describe('connect', () => {
+    it('should throw error when pool creation fails', async () => {
+      mockPgPool.connect.mockRejectedValue(new Error('connection refused'))
+      const svc = new PostgreSqlService(mockConfig)
+      await expect(svc.connect()).rejects.toThrow('Failed to connect to PostgreSQL')
+    })
+
+    it('should establish connection and release test client', async () => {
+      await service.connect()
+      expect(mockPgPool.connect).toHaveBeenCalled()
+      expect(mockPgClient.release).toHaveBeenCalled()
+      expect(service.isConnected()).toBe(true)
+    })
+
+    it('should throw when already connected', async () => {
+      await service.connect()
+      await expect(service.connect()).rejects.toThrow('Already connected to PostgreSQL')
+    })
+
+    it('should reset pool to null on connection failure', async () => {
+      mockPgPool.connect.mockRejectedValue(new Error('timeout'))
+      await expect(service.connect()).rejects.toThrow('Failed to connect to PostgreSQL')
+      expect(service.isConnected()).toBe(false)
+    })
+  })
+
   describe('query', () => {
     it('should throw error when not connected', async () => {
       await expect(service.query('SELECT 1')).rejects.toThrow('Not connected to PostgreSQL')
     })
+
+    it('should execute query and return rows with columns', async () => {
+      await service.connect()
+      mockPgPool.query.mockResolvedValue({
+        rows: [{ ID: 1, Name: 'test' }],
+        fields: [{ name: 'ID' }, { name: 'Name' }],
+        rowCount: 1
+      })
+
+      const result = await service.query('SELECT ID, Name FROM Users')
+
+      expect(result.rows).toEqual([{ ID: 1, Name: 'test' }])
+      expect(result.columns).toEqual(['ID', 'Name'])
+      expect(result.rowCount).toBe(1)
+    })
+
+    it('should pass params through to pool.query', async () => {
+      await service.connect()
+      mockPgPool.query.mockResolvedValue({ rows: [], fields: [], rowCount: 0 })
+
+      await service.query('SELECT * FROM Users WHERE ID = $1', [42])
+
+      expect(mockPgPool.query).toHaveBeenCalledWith(expect.any(String), [42])
+    })
+
+    it('should fallback to rows.length when rowCount is null', async () => {
+      await service.connect()
+      mockPgPool.query.mockResolvedValue({
+        rows: [{ ID: 1 }, { ID: 2 }],
+        fields: [{ name: 'ID' }],
+        rowCount: null
+      })
+
+      const result = await service.query('SELECT ID FROM Users')
+      expect(result.rowCount).toBe(2)
+    })
+
+    it('should wrap query errors with context', async () => {
+      await service.connect()
+      mockPgPool.query.mockRejectedValue(new Error('syntax error'))
+
+      await expect(service.query('INVALID SQL')).rejects.toThrow('PostgreSQL query failed')
+    })
   })
 
   describe('transaction', () => {
@@ -52,13 +163,36 @@ describe('PostgreSqlService Unit Tests', () => {
         'Not connected to PostgreSQL'
       )
     })
-  })
 
-  describe('connect', () => {
-    it('should throw error with invalid host', async () => {
-      const invalidConfig = { ...mockConfig, host: 'invalid-host-that-does-not-exist' }
-      const invalidService = new PostgreSqlService(invalidConfig)
-      await expect(invalidService.connect()).rejects.toThrow('Failed to connect to PostgreSQL')
+    it('should execute all queries within BEGIN/COMMIT and release client', async () => {
+      await service.connect()
+      mockPgClient.query.mockResolvedValue({ rows: [] })
+
+      await service.transaction([
+        { sql: 'SELECT 1', params: [1] },
+        { sql: 'SELECT 2' }
+      ])
+
+      // BEGIN + 2 queries + COMMIT
+      expect(mockPgClient.query).toHaveBeenCalledTimes(4)
+      expect(mockPgClient.query).toHaveBeenNthCalledWith(1, 'BEGIN')
+      expect(mockPgClient.query).toHaveBeenNthCalledWith(4, 'COMMIT')
+      expect(mockPgClient.release).toHaveBeenCalled()
+    })
+
+    it('should rollback and release client on query failure', async () => {
+      await service.connect()
+      mockPgClient.query
+        .mockResolvedValueOnce({ rows: [] }) // BEGIN
+        .mockRejectedValueOnce(new Error('constraint violation')) // query fails
+        .mockResolvedValueOnce({ rows: [] }) // ROLLBACK
+
+      await expect(
+        service.transaction([{ sql: 'SELECT 1', params: [1] }])
+      ).rejects.toThrow('PostgreSQL transaction failed')
+
+      expect(mockPgClient.query).toHaveBeenCalledWith('ROLLBACK')
+      expect(mockPgClient.release).toHaveBeenCalled()
     })
   })
 
@@ -66,6 +200,23 @@ describe('PostgreSqlService Unit Tests', () => {
     it('should resolve when not connected', async () => {
       await expect(service.disconnect()).resolves.not.toThrow()
     })
+
+    it('should end pool and reset state', async () => {
+      await service.connect()
+      expect(service.isConnected()).toBe(true)
+
+      await service.disconnect()
+
+      expect(mockPgPool.end).toHaveBeenCalled()
+      expect(service.isConnected()).toBe(false)
+    })
+
+    it('should wrap disconnect errors', async () => {
+      await service.connect()
+      mockPgPool.end.mockRejectedValue(new Error('pool end failed'))
+
+      await expect(service.disconnect()).rejects.toThrow('Failed to disconnect from PostgreSQL')
+    })
   })
 })
 
@@ -83,7 +234,8 @@ describe('prepareSql', () => {
   })
 
   it('should quote column names in INSERT', () => {
-    const sql = 'INSERT INTO "dbo"."BIPUsers" (UserName, Password, UserType) VALUES ($1, $2, $3)'
+    const sql =
+      'INSERT INTO "dbo"."BIPUsers" (UserName, Password, UserType) VALUES ($1, $2, $3)'
     const result = prepareSql(sql)
     expect(result).toBe(
       'INSERT INTO "dbo"."BIPUsers" ("UserName", "Password", "UserType") VALUES ($1, $2, $3)'
@@ -151,7 +303,9 @@ describe('prepareSql', () => {
   it('should quote underscore-containing column names', () => {
     const sql = 'SELECT ERP_URL, ERP_Username, ERP_Password FROM "dbo"."BIPUsers"'
     const result = prepareSql(sql)
-    expect(result).toBe('SELECT "ERP_URL", "ERP_Username", "ERP_Password" FROM "dbo"."BIPUsers"')
+    expect(result).toBe(
+      'SELECT "ERP_URL", "ERP_Username", "ERP_Password" FROM "dbo"."BIPUsers"'
+    )
   })
 
   it('should handle ON CONFLICT DO UPDATE SET with EXCLUDED', () => {
diff --git a/tests/unit/sql-server.test.ts b/tests/unit/sql-server.test.ts
index 692db4e..5f00ccc 100644
--- a/tests/unit/sql-server.test.ts
+++ b/tests/unit/sql-server.test.ts
@@ -1,11 +1,82 @@
 /**
  * Unit tests for SqlServerService
- * These tests do not require a SQL Server instance
+ * Covers both unconnected state and connected-path operations using mocked mssql driver.
  */
 
-import { describe, it, expect, beforeEach } from 'vitest'
+import { describe, it, expect, beforeEach, vi } from 'vitest'
 import { SqlServerService } from '@main/services/database/sql-server'
 
+// ---- Hoisted mock functions ----
+const {
+  mockPoolConnect,
+  mockPoolClose,
+  mockRequestInput,
+  mockRequestQuery,
+  mockTransactionBegin,
+  mockTransactionCommit,
+  mockTransactionRollback,
+  mockPool,
+  mockRequest,
+  mockTransaction
+} = vi.hoisted(() => {
+  const request = {
+    input: vi.fn(),
+    query: vi.fn()
+  }
+  const transaction = {
+    begin: vi.fn(),
+    commit: vi.fn(),
+    rollback: vi.fn()
+  }
+  const pool = {
+    connect: vi.fn(),
+    request: vi.fn(() => request),
+    close: vi.fn(),
+    connected: true
+  }
+  return {
+    mockPoolConnect: pool.connect,
+    mockPoolClose: pool.close,
+    mockRequestInput: request.input,
+    mockRequestQuery: request.query,
+    mockTransactionBegin: transaction.begin,
+    mockTransactionCommit: transaction.commit,
+    mockTransactionRollback: transaction.rollback,
+    mockPool: pool,
+    mockRequest: request,
+    mockTransaction: transaction
+  }
+})
+
+// Mock mssql driver (must use regular functions because source uses `new`)
+vi.mock('mssql', () => ({
+  default: {
+    ConnectionPool: vi.fn(function () {
+      return mockPool
+    }),
+    Transaction: vi.fn(function () {
+      return mockTransaction
+    }),
+    Request: vi.fn(function () {
+      return mockRequest
+    })
+  }
+}))
+
+// Mock logger
+vi.mock('@main/services/logger', () => ({
+  createLogger: () => ({
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+    debug: vi.fn()
+  }),
+  trackDuration: async <T>(fn: () => Promise<T>) => {
+    const result = await fn()
+    return { result }
+  }
+}))
+
 const mockConfig = {
   server: 'localhost',
   port: 1433,
@@ -22,6 +93,18 @@ describe('SqlServerService Unit Tests', () => {
   let service: SqlServerService
 
   beforeEach(() => {
+    vi.clearAllMocks()
+    mockPool.connected = true
+    mockPoolConnect.mockResolvedValue(undefined)
+    mockPoolClose.mockResolvedValue(undefined)
+    mockRequestInput.mockReturnThis()
+    mockRequestQuery.mockResolvedValue({
+      recordset: [],
+      rowsAffected: [0]
+    })
+    mockTransactionBegin.mockResolvedValue(undefined)
+    mockTransactionCommit.mockResolvedValue(undefined)
+    mockTransactionRollback.mockResolvedValue(undefined)
     service = new SqlServerService(mockConfig)
   })
 
@@ -39,15 +122,22 @@ describe('SqlServerService Unit Tests', () => {
   })
 
   describe('connect', () => {
-    it('should throw error with invalid credentials', async () => {
-      // This tests error handling without needing a real server
-      const invalidConfig = {
-        ...mockConfig,
-        server: 'invalid-host-that-does-not-exist'
-      }
-      const invalidService = new SqlServerService(invalidConfig)
+    it('should throw error when connection fails', async () => {
+      mockPool.connected = false
+      mockPoolConnect.mockRejectedValue(new Error('connection refused'))
+      const svc = new SqlServerService(mockConfig)
+      await expect(svc.connect()).rejects.toThrow('Failed to connect to SQL Server')
+    })
 
-      await expect(invalidService.connect()).rejects.toThrow('Failed to connect to SQL Server')
+    it('should establish connection via pool', async () => {
+      await service.connect()
+      expect(mockPoolConnect).toHaveBeenCalled()
+      expect(service.isConnected()).toBe(true)
+    })
+
+    it('should throw when already connected', async () => {
+      await service.connect()
+      await expect(service.connect()).rejects.toThrow('Already connected to SQL Server')
     })
   })
 
@@ -55,6 +145,87 @@ describe('SqlServerService Unit Tests', () => {
     it('should throw error when not connected', async () => {
       await expect(service.query('SELECT 1')).rejects.toThrow('Not connected to SQL Server')
     })
+
+    it('should execute SELECT and return rows with columns', async () => {
+      await service.connect()
+      mockRequestQuery.mockResolvedValue({
+        recordset: [{ ID: 1, Name: 'test' }, { ID: 2, Name: 'foo' }],
+        rowsAffected: [2]
+      })
+
+      const result = await service.query('SELECT ID, Name FROM Users')
+
+      expect(mockRequestQuery).toHaveBeenCalledWith('SELECT ID, Name FROM Users')
+      expect(result.rows).toEqual([
+        { ID: 1, Name: 'test' },
+        { ID: 2, Name: 'foo' }
+      ])
+      expect(result.columns).toEqual(['ID', 'Name'])
+      expect(result.rowCount).toBe(2)
+    })
+
+    it('should convert array params to @p0, @p1, ... format', async () => {
+      await service.connect()
+      mockRequestQuery.mockResolvedValue({ recordset: [], rowsAffected: [0] })
+
+      await service.query('SELECT * FROM Users WHERE ID = @p0 AND Name = @p1', [42, 'test'])
+
+      expect(mockRequestInput).toHaveBeenCalledWith('p0', 42)
+      expect(mockRequestInput).toHaveBeenCalledWith('p1', 'test')
+    })
+
+    it('should handle INSERT/UPDATE with rowsAffected', async () => {
+      await service.connect()
+      mockRequestQuery.mockResolvedValue({
+        recordset: undefined,
+        rowsAffected: [5]
+      })
+
+      const result = await service.query('DELETE FROM Users WHERE Active = 0')
+
+      expect(result.rows).toEqual([])
+      expect(result.columns).toEqual([])
+      expect(result.rowCount).toBe(5)
+    })
+
+    it('should fallback to rows.length when rowsAffected is missing', async () => {
+      await service.connect()
+      mockRequestQuery.mockResolvedValue({
+        recordset: [{ ID: 1 }, { ID: 2 }],
+        rowsAffected: undefined
+      })
+
+      const result = await service.query('SELECT ID FROM Users')
+      expect(result.rowCount).toBe(2)
+    })
+
+    it('should wrap query errors with context', async () => {
+      await service.connect()
+      mockRequestQuery.mockRejectedValue(new Error('syntax error'))
+
+      await expect(service.query('INVALID SQL')).rejects.toThrow('SQL Server query failed')
+    })
+  })
+
+  describe('queryWithParams', () => {
+    it('should throw error when not connected', async () => {
+      await expect(
+        service.queryWithParams('SELECT @p0', { p0: { value: 1 } })
+      ).rejects.toThrow('Not connected to SQL Server')
+    })
+
+    it('should add typed params via request.input', async () => {
+      await service.connect()
+      mockRequestQuery.mockResolvedValue({ recordset: [{ ID: 1 }], rowsAffected: [1] })
+
+      await service.queryWithParams('SELECT @id', {
+        id: { value: 42 },
+        name: { value: 'test', type: 'NVarChar' as any }
+      })
+
+      expect(mockRequestInput).toHaveBeenCalledWith('id', 42)
+      expect(mockRequestInput).toHaveBeenCalledWith('name', 'NVarChar', 'test')
+    })
   })
 
   describe('transaction', () => {
@@ -63,11 +234,56 @@ describe('SqlServerService Unit Tests', () => {
         'Not connected to SQL Server'
       )
     })
+
+    it('should execute all queries and commit', async () => {
+      await service.connect()
+      mockRequestQuery.mockResolvedValue({ recordset: [], rowsAffected: [1] })
+
+      await service.transaction([
+        { sql: 'INSERT INTO t VALUES (@p0)', params: [1] },
+        { sql: 'UPDATE t SET x = 1' }
+      ])
+
+      expect(mockTransactionBegin).toHaveBeenCalled()
+      expect(mockRequestQuery).toHaveBeenCalledTimes(2)
+      expect(mockRequestInput).toHaveBeenCalledWith('p0', 1)
+      expect(mockTransactionCommit).toHaveBeenCalled()
+      expect(mockTransactionRollback).not.toHaveBeenCalled()
+    })
+
+    it('should rollback on query failure', async () => {
+      await service.connect()
+      mockRequestQuery.mockRejectedValue(new Error('constraint violation'))
+
+      await expect(
+        service.transaction([{ sql: 'INSERT INTO t VALUES (@p0)', params: [1] }])
+      ).rejects.toThrow('SQL Server transaction failed')
+
+      expect(mockTransactionRollback).toHaveBeenCalled()
+      expect(mockTransactionCommit).not.toHaveBeenCalled()
+    })
   })
 
   describe('disconnect', () => {
     it('should resolve when not connected', async () => {
       await expect(service.disconnect()).resolves.not.toThrow()
     })
+
+    it('should close pool and reset state', async () => {
+      await service.connect()
+      expect(service.isConnected()).toBe(true)
+
+      await service.disconnect()
+
+      expect(mockPoolClose).toHaveBeenCalled()
+      expect(service.isConnected()).toBe(false)
+    })
+
+    it('should wrap disconnect errors', async () => {
+      await service.connect()
+      mockPoolClose.mockRejectedValue(new Error('pool close failed'))
+
+      await expect(service.disconnect()).rejects.toThrow('Failed to disconnect from SQL Server')
+    })
   })
 })
diff --git a/vitest.config.ts b/vitest.config.ts
index 910f3cc..f8564fa 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -6,13 +6,13 @@ export default defineConfig({
     globals: true,
     environment: 'node',
     include: ['tests/**/*.{test,spec}.{ts,tsx}'],
-    exclude: ['node_modules', 'dist', 'out', 'tests/e2e'],
+    exclude: ['node_modules', 'dist', 'out', 'tests/e2e', 'tests/integration'],
     setupFiles: ['tests/setup.ts'],
     env: {
       NODE_ENV: 'test'
     },
-    // 性能优化配置
-    isolate: false, // 禁用隔离（提升 30-50% 速度）
+    // CI 环境启用隔离以捕获跨文件状态污染；本地开发禁用以提升速度
+    isolate: !!process.env.CI,
     pool: 'threads', // 使用线程池
     maxWorkers: 4,
     bail: process.env.CI ? 1 : undefined,