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Implement generic context (#60)
* Add generic Context class * Context can fetch single values * Remove Context::setCurrent * Add @internal annotation for Context::reset() * Add ability to set multiple context values at once
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‎src/Core/Context.php‎

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<?php
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/**
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* Copyright 2017 OpenCensus Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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namespace OpenCensus\Core;
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/**
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* This class is an implementation of a generic context.
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*
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* Example:
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* ```
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* // Create and set a new context, which inherits values from the current
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* // context and adds a new key/value pair of 'foo'/'bar'.
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* $prev = Context::current()->withValue('foo', 'bar')->attach();
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* try {
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* // Do something within the context
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* } finally {
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* // This makes sure that $prev will be current after this execution
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* Context::current()->detach($prev);
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* }
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* // Here, we are 100% sure $prev is the current context.
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* ```
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*/
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class Context
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{
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/**
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* @var Context
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*/
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private static $current;
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/**
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* @var array
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*/
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private $values;
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/**
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* Creates a new Context.
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*
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* @param array $initialValues
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*/
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public function __construct($initialValues = [])
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{
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$this->values = $initialValues;
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}
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/**
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* Creates a new context with the given key/value set.
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*
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* @param string $key
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* @param mixed $value
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* @return Context
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*/
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public function withValue($key, $value)
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{
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$copy = $this->values;
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$copy[$key] = $value;
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return new Context($copy);
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}
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/**
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* Creates a new context with the given key/values.
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*
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* @param array $data
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* @return Context
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*/
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public function withValues($data)
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{
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$copy = $this->values;
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foreach ($data as $key => $value) {
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$copy[$key] = $value;
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}
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return new Context($copy);
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}
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/**
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* Fetches the value for a given key in this context. Returns the provided
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* default if not set.
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*
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* @param string $key
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* @param mixed $default [optional]
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* @return mixed
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*/
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public function value($key, $default = null)
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{
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return array_key_exists($key, $this->values)
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? $this->values[$key]
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: $default;
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}
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/**
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* Attaches this context, thus entering a new scope within which this
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* context is current(). The previously current context is returned.
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*
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* @return Context
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*/
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public function attach()
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{
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$current = self::current();
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self::$current = $this;
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return $current;
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}
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/**
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* Reverses an attach(), restoring the previous context and exiting the
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* current scope.
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*
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* @param Context $toAttach
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*/
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public function detach(Context $toAttach)
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{
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if (self::current() !== $this) {
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trigger_error('Unexpected context to detach.', E_USER_WARNING);
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}
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self::$current = $toAttach;
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}
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/**
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* Returns all the contained data.
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*
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* @return array
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*/
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public function values()
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{
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return $this->values;
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}
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/**
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* Returns the context associated with the current scope, will never return
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* null.
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*
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* @return Context
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*/
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public static function current()
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{
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if (!self::$current) {
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self::$current = self::background();
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}
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return self::$current;
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}
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/**
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* Returns an empty context.
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*
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* @return Context
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*/
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public static function background()
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{
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return new Context();
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}
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/**
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* Resets the context to an initial state. This is generally used only for
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* testing.
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*
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* @internal
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*/
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public static function reset()
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{
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self::$current = null;
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}
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}

‎tests/unit/Core/ContextTest.php‎

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<?php
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/**
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* Copyright 2017 OpenCensus Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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namespace OpenCensus\Tests\Unit\Core;
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use OpenCensus\Core\Context;
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/**
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* @group core
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*/
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class ContextTest extends \PHPUnit_Framework_TestCase
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{
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public function setUp()
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{
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Context::reset();
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}
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public function tearDown()
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{
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Context::reset();
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}
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public function testBackgroundGeneratesEmptyContext()
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{
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$context = Context::background();
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$this->assertInstanceOf(Context::class, $context);
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$this->assertEquals([], $context->values());
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}
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public function testCurrentAlwaysReturnsAContext()
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{
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$context = Context::current();
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$this->assertInstanceOf(Context::class, $context);
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}
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public function testAttachingCurrentContext()
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{
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$context = new Context(['foo' => 'bar']);
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$prevContext = $context->attach();
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$current = Context::current();
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$this->assertInstanceOf(Context::class, $current);
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$this->assertEquals($context, $current);
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}
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public function testRestoringCurrentContext()
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{
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$context = new Context(['foo' => 'bar']);
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$prevContext = $context->attach();
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Context::current()->detach($prevContext);
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}
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/**
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* @expectedException PHPUnit_Framework_Error_Warning
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*/
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public function testRestoringCurrentContextRequiresSameObject()
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{
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$context = new Context(['foo' => 'bar']);
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$prevContext = $context->attach();
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$other = new Context(['foo' => 'bar']);
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$this->assertFalse($prevContext === $other);
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$other->detach($other);
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}
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public function testContextValuesAreCopied()
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{
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$data = ['foo' => 'bar'];
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$context = new Context($data);
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$data['foo'] = 'asdf';
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$this->assertNotEquals($data, $context->values());
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}
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public function testWithValueInheritsPreviousContext()
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{
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$context = new Context(['foo' => 'bar']);
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$newContext = $context->withValue('asdf', 'qwer');
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$this->assertEquals(['foo' => 'bar', 'asdf' => 'qwer'], $newContext->values());
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}
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public function testChangingExistingValueDoesNotAffectOtherContexts()
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{
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$context = new Context(['foo' => 'bar']);
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$newContext = $context->withValue('foo', 'baz');
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$this->assertEquals(['foo' => 'baz'], $newContext->values());
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$this->assertEquals(['foo' => 'bar'], $context->values());
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}
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public function testFetchingExistingValue()
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{
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$context = new Context(['foo' => 'bar']);
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$this->assertEquals('bar', $context->value('foo'));
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}
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public function testFetchingNonExistentValue()
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{
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$context = new Context();
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$this->assertNull($context->value('foo'));
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}
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public function testFetchingNonExistentValueWithDefault()
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{
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$default = 'bar';
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$context = new Context();
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$this->assertEquals($default, $context->value('foo', $default));
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}
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public function testApplyMultipleValues()
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{
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$context = new Context(['foo' => 'bar']);
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$newContext = $context->withValues([
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'asdf' => 'qwer',
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'zxcv' => 'jkl;'
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]);
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$this->assertEquals(['foo' => 'bar', 'asdf' => 'qwer', 'zxcv' => 'jkl;'], $newContext->values());
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}
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}

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