test: add tests for upgrade-sensitive areas

- Token model structure: verify $casts has datetime fields, $fillable
  is complete, and $table is set correctly (catches $dates→$casts regression)
- ClientServiceProvider: verify DeferrableProvider interface is
  implemented and provides() returns Client::class (catches $defer regression)
- Token parseOauthToken: verify stored values and Carbon types, not
  just that mock methods were called
- Client setToken: verify DataService cache is cleared on token change
- Client delegation: verify hasValidAccessToken/hasValidRefreshToken
  delegate to Token correctly

tests/ClientTest.php

@@ -145,3 +145,54 @@
 
     expect($this->client->deleteToken())->toBeInstanceOf(Client::class);
 });
+
+it('clears cached data service when token is changed', function () {
+    $this->token_mock
+        ->shouldReceive('getAttribute')
+        ->with('hasValidAccessToken')
+        ->andReturnFalse();
+
+    $this->token_mock
+        ->shouldReceive('getAttribute')
+        ->with('hasValidRefreshToken')
+        ->andReturnFalse();
+
+    $first = $this->client->getDataService();
+
+    $new_token = Mockery::mock(Token::class);
+    $new_token
+        ->shouldReceive('getAttribute')
+        ->with('hasValidAccessToken')
+        ->andReturnFalse();
+
+    $new_token
+        ->shouldReceive('getAttribute')
+        ->with('hasValidRefreshToken')
+        ->andReturnFalse();
+
+    $this->client->setToken($new_token);
+
+    $second = $this->client->getDataService();
+
+    expect($second)->not->toBe($first);
+});
+
+it('delegates hasValidAccessToken to token', function () {
+    $this->token_mock
+        ->shouldReceive('getAttribute')
+        ->once()
+        ->with('hasValidAccessToken')
+        ->andReturnTrue();
+
+    expect($this->client->hasValidAccessToken())->toBeTrue();
+});
+
+it('delegates hasValidRefreshToken to token', function () {
+    $this->token_mock
+        ->shouldReceive('getAttribute')
+        ->once()
+        ->with('hasValidRefreshToken')
+        ->andReturnFalse();
+
+    expect($this->client->hasValidRefreshToken())->toBeFalse();
+});

tests/TokenModelTest.php

@@ -0,0 +1,49 @@
+<?php
+
+use Illuminate\Contracts\Support\DeferrableProvider;
+use Wearepixel\QuickBooks\Client;
+use Wearepixel\QuickBooks\Providers\ClientServiceProvider;
+use Wearepixel\QuickBooks\Token;
+
+describe('Token model structure', function () {
+    it('uses the quickbooks_tokens table', function () {
+        expect((new Token)->getTable())->toBe('quickbooks_tokens');
+    });
+
+    it('casts expiration fields to datetime', function () {
+        $casts = (new Token)->getCasts();
+
+        expect($casts)
+            ->toHaveKey('access_token_expires_at', 'datetime')
+            ->toHaveKey('refresh_token_expires_at', 'datetime');
+    });
+
+    it('has all expected fillable attributes', function () {
+        $fillable = (new Token)->getFillable();
+
+        expect($fillable)->toEqualCanonicalizing([
+            'access_token',
+            'access_token_expires_at',
+            'realm_id',
+            'refresh_token',
+            'refresh_token_expires_at',
+            'user_id',
+        ]);
+    });
+});
+
+describe('ClientServiceProvider structure', function () {
+    it('implements DeferrableProvider', function () {
+        expect(ClientServiceProvider::class)
+            ->toImplement(DeferrableProvider::class);
+    });
+
+    it('declares Client in provides array', function () {
+        $app = Mockery::mock(\Illuminate\Contracts\Foundation\Application::class);
+        $app->shouldIgnoreMissing();
+
+        $provider = new ClientServiceProvider($app);
+
+        expect($provider->provides())->toBe([Client::class]);
+    });
+});

tests/TokenTest.php

@@ -70,12 +70,19 @@
     $oauth_token_mock = Mockery::mock(QuickBooksOnline\API\Core\OAuth\OAuth2\OAuth2AccessToken::class);
 
     $oauth_token_mock->shouldReceive('getAccessToken')->once()->withNoArgs()->andReturn('access_token');
-    $oauth_token_mock->shouldReceive('getAccessTokenExpiresAt')->once()->withNoArgs()->andReturn('now');
+    $oauth_token_mock->shouldReceive('getAccessTokenExpiresAt')->once()->withNoArgs()->andReturn('2025-06-15 12:00:00');
     $oauth_token_mock->shouldReceive('getRealmID')->once()->withNoArgs()->andReturn('realm_id');
     $oauth_token_mock->shouldReceive('getRefreshToken')->once()->withNoArgs()->andReturn('refresh_token');
-    $oauth_token_mock->shouldReceive('getRefreshTokenExpiresAt')->once()->withNoArgs()->andReturn('now');
+    $oauth_token_mock->shouldReceive('getRefreshTokenExpiresAt')->once()->withNoArgs()->andReturn('2025-09-24 12:00:00');
 
-    $this->token->parseOauthToken($oauth_token_mock);
+    $result = $this->token->parseOauthToken($oauth_token_mock);
+
+    expect($result)->toBeInstanceOf(Token::class)
+        ->and($this->token->access_token)->toBe('access_token')
+        ->and($this->token->realm_id)->toBe('realm_id')
+        ->and($this->token->refresh_token)->toBe('refresh_token')
+        ->and($this->token->access_token_expires_at)->toBeInstanceOf(Carbon::class)
+        ->and($this->token->refresh_token_expires_at)->toBeInstanceOf(Carbon::class);
 });
 
 it('allows itself to be deleted and returns new token', function () {