Add source class

src/spectator/includes.cr

@@ -42,4 +42,5 @@ require "./pending_result"
 require "./failed_result"
 require "./errored_result"
 
+require "./source"
 require "./example_iterator"

src/spectator/source.cr

@@ -0,0 +1,22 @@
+module Spectator
+  # Define the file and line number something originated from.
+  struct Source
+    # Absolute file path.
+    getter file : String
+
+    # Line number in the file.
+    getter line : Int32
+
+    # Creates the source.
+    def initialize(@file, @line)
+    end
+
+    # String representation of the source.
+    # This is formatted as `FILE:LINE`.
+    def to_s(io)
+      io << file
+      io << ':'
+      io << line
+    end
+  end
+end