From 8ae6ef478b2883ec632a46fb3053e5d3a731d97c Mon Sep 17 00:00:00 2001
From: Michael Miller <icy.arctic.fox@gmail.com>
Date: Sat, 7 Nov 2020 14:43:59 -0700
Subject: [PATCH] Dynamic examples with null context

---
 src/spectator/example.cr                  | 11 +++++++++++
 src/spectator/example_context_delegate.cr | 10 ++++++++++
 src/spectator/example_context_method.cr   |  3 +--
 src/spectator/null_context.cr             |  6 ++++++
 4 files changed, 28 insertions(+), 2 deletions(-)
 create mode 100644 src/spectator/null_context.cr

diff --git a/src/spectator/example.cr b/src/spectator/example.cr
index 6cc630c..2f435e6 100644
--- a/src/spectator/example.cr
+++ b/src/spectator/example.cr
@@ -26,6 +26,17 @@ module Spectator
       super(name, source, group)
     end
 
+    # Creates a dynamic example.
+    # A block provided to this method will be called as-if it were the test code for the example.
+    # The block will be given this example instance as an argument.
+    # The *name* describes the purpose of the example.
+    # It can be a `Symbol` to describe a type.
+    # The *source* tracks where the example exists in source code.
+    # The example will be assigned to *group* if it is provided.
+    def initialize(name : String? = nil, source : Source? = nil, group : ExampleGroup? = nil, &block : Example -> _)
+      @delegate = ExampleContextDelegate.null(&block)
+    end
+
     # Executes the test case.
     # Returns the result of the execution.
     # The result will also be stored in `#result`.
diff --git a/src/spectator/example_context_delegate.cr b/src/spectator/example_context_delegate.cr
index bd5aa9c..cd8f6bb 100644
--- a/src/spectator/example_context_delegate.cr
+++ b/src/spectator/example_context_delegate.cr
@@ -1,5 +1,6 @@
 require "./context"
 require "./example_context_method"
+require "./null_context"
 
 module Spectator
   # Stores a test context and a method to call within it.
@@ -11,6 +12,15 @@ module Spectator
     def initialize(@context : Context, @method : ExampleContextMethod)
     end
 
+    # Creates a delegate with a null context.
+    # The context will be ignored and the block will be executed in its original scope.
+    # The example instance will be provided as an argument to the block.
+    def self.null(&block : Example -> _)
+      context = NullContext.new
+      method = ExampleContextMethod.new { |example| block.call(example) }
+      new(context, method)
+    end
+
     # Invokes a method in the test context.
     # The *example* is the current running example.
     def call(example : Example)
diff --git a/src/spectator/example_context_method.cr b/src/spectator/example_context_method.cr
index a3e3dfc..c14d254 100644
--- a/src/spectator/example_context_method.cr
+++ b/src/spectator/example_context_method.cr
@@ -4,8 +4,7 @@ module Spectator
   # Encapsulates a method in a test context.
   # This could be used to invoke a test case or hook method.
   # The context is passed as an argument.
-  # The proc should downcast the context instance to the desired type
-  # and call a method on that context.
+  # The proc should downcast the context instance to the desired type and call a method on that context.
   # The current example is also passed as an argument.
   alias ExampleContextMethod = Example, Context ->
 end
diff --git a/src/spectator/null_context.cr b/src/spectator/null_context.cr
new file mode 100644
index 0000000..3597203
--- /dev/null
+++ b/src/spectator/null_context.cr
@@ -0,0 +1,6 @@
+module Spectator
+  # Empty context used to construct examples that don't have contexts.
+  # This is useful for dynamically creating examples outside of a spec.
+  class NullContext < Context
+  end
+end