apply O'Reilly conventions, add missing word

Co-authored-by: Harry Percival <[email protected]>

Author: Xronophobe

chapter_12_organising_test_files.asciidoc

@@ -568,8 +568,8 @@ saves you from having to use `def..():` and an indented block:
 5
 ----
 
-In our case, we're using it to transform a bit of code - that would otherwise be
-executed immediately - into a function that we can pass as an argument,
+In our case, we're using it to transform a bit of code--that would otherwise be
+executed immediately--into a function that we can pass as an argument,
 and that can be executed later, and multiple times:
 // CSANAD: I think it's easier to read like this.
 
@@ -632,14 +632,14 @@ through what happened:
 <1> In our FT, we call our `self.wait_for` helper, where we pass
     the `lambda`-ified version of `assertEqual`.
 
-<2> We go into `self.wait_for` in `base.py`,
+<2> We go into `self.wait_for` in _base.py_,
     where we're calling (and returning) `fn()`, which refers to the passed
     lambda function encapsulating our test assertion.
 
 <3> To explain where the exception has actually come from,
     the traceback takes us back into _test_list_item_validation.py_
     and inside the body of the `lambda` function,
-    and tells us that the attempt to find the `.invalid-feedback` element
+    and tells us that it was attempt to find the `.invalid-feedback` element
     that failed.
 // CSANAD: I changed two things here:
 //   First, I think it's better to remove the specific line number which may