test(depinject): add preference feature

depinject/features/prefer.feature

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+Feature: interface type resolution
+
+  Background:
+    Given an interface Duck
+    And two implementations Mallard and Canvasback
+
+  Rule: interface types resolve to a concrete type implicitly if there is only one matching implementation
+    Example: only one implementation
+      Given "Mallard" is provided
+      When we try to resolve a "Duck" in global scope
+      Then "Mallard" is resolved in global scope
+
+    Example: two implementations
+      Given "Mallard" and "Canvasback" are provided
+      When we try to resolve a "Duck" in global scope
+      Then there is a "multiple implicit interface bindings" error
+
+  Rule: preferences must point to a real type
+    Example:
+      Given "Mallard" is provided
+      And there is a global preference for a "Marbled" "Duck"
+      When we try to resolve a "Duck" in global scope
+      Then there is a "no type for explicit binding" error
+
+  Rule: preferences supersede implicit type resolution
+    Example: global scope
+      Given "Canvasback" is provided
+      And there is a global preference for a "Mallard" "Duck"
+      When we try to resolve a "Duck" in global scope
+      Then there is a "can't resolve" error
+
+    Example: module scope
+      Given "Canvasback" is provided
+      And there is a preference for a "Mallard" "Duck" in module "A"
+      When module "A" wants a "Duck"
+      Then there is a "can't resolve" error
+
+  Rule: preferences in global scope apply to both global and module-scoped resolution (if there is no module-scoped preference)
+    Example: global resolution
+      Given "Mallard" and "Canvasback" are provided
+      And there is a global preference for a "Mallard" "Duck"
+      When we try to resolve a "Duck" in global scope
+      Then "Mallard" is resolved in global scope
+
+    Example: module-scoped resolution
+      Given "Mallard" and "Canvasback" are provided
+      And there is a global preference for a "Mallard" "Duck"
+      When module "A" wants a "Duck"
+      Then module "A" resolves a "Mallard"
+
+  Rule: module-scoped preferences only apply to module-scoped resolution
+    Example: a module-scoped binding doesn't work for global scope
+      Given "Mallard" and "Canvasback" are provided
+      And there is a preference for a "Canvasback" "Duck" in module "A"
+      When we try to resolve a "Duck" in global scope
+      Then there is a "multiple implicit interface bindings" error
+
+    Example: a module-scoped binding works for that module
+      Given "Mallard" and "Canvasback" are provided
+      And there is a preference for a "Canvasback" "Duck" in module "A"
+      When module "A" wants a "Duck"
+      Then module "A" resolves a "Canvasback"
+
+    Example: a module-scoped binding doesn't work for another module
+      Given "Mallard" and "Canvasback" are provided
+      And there is a preference for a "Canvasback" "Duck" in module "A"
+      When module "B" wants a "Duck"
+      Then there is a "multiple implicit interface bindings" error
+
+    # this case is called a "journey" scenario which tests a bunch of things together
+    # most tests should be short and to the point like the ones above but one or two long ones
+    # are good to test more things together &/or do integration tests
+    Example: two module-scoped preferences and a global preference
+      Given "Mallard" and "Canvasback" are provided
+      * there is a global preference for a "Mallard" "Duck"
+      * there is a preference for a "Canvasback" "Duck" in module "A"
+      * there is a preference for a "Mallard" "Duck" in module "B"
+      When module "A" wants a "Duck"
+      * module "B" wants a "Duck"
+      * module "C" wants a "Duck"
+      Then module "A" resolves a "Canvasback"
+      * module "B" resolves a "Mallard"
+      * module "C" resolves a "Mallard"
+      * "Mallard" is resolved in global scope