Context class does not use typed data trait correctly, leading to fatal errors

1. +++ b/core/lib/Drupal/Core/Plugin/Context/Context.php
   @@ -46,7 +46,7 @@ public function getContextValue() {
   -    return $this->typedDataManager->getCanonicalRepresentation($this->contextData);
   +    return $this->getTypedDataManager()->getCanonicalRepresentation($this->contextData);
   

   ouch, yes - totally.

2. +++ b/core/modules/system/src/Tests/Context/ContextIntegrationTest.php
   @@ -0,0 +1,40 @@
   +   * This test ensures that the typed data manager is set correctly on the
   +   * Context class. We cannot test this with a PHPUnit test because we want to
   +   * make sure that the TypedDataTrait works correctly on the Context class.
   

   I do not get this reasoning - why shouldn't it be possible to the test this with phpunit?

   Also, the test case is named a bit weird. integrating with what? Maybe, it should be called ContextTypedDataTest to ensure context works properly with typed data in general?

+++ b/core/tests/Drupal/Tests/Core/Plugin/Context/ContextTypedDataTest.php
@@ -0,0 +1,54 @@
+    $typed_data_manager->expects($this->once())
+      ->method('getCanonicalRepresentation')
+      ->willReturn($typed_data);

Thanks, code looks good now except this:

That's cheating. It should be able to return the right value from setting it. Also, the canonical representation for strings is the string.
I think best, you'd set a callback as getCanonicalRepresentation() on the TDM mock which just returns the string. Then, the test should check that the returned context value really is a plain string - it's a test for getContextValue() after all.

Thanks, the test makes sense to me like that now.

Added tag as this causes failures in Rules.

Nice catch. Sounds major to me.

Committed and pushed to 8.0.x. Thanks!