guides, bring back minitest assertion table. [ci skip]

Rails has different naming conventions for the inverse assertion
methods. While minitest uses `refute` we use `_not`. We should have a
table listing the common assertions that you want to use in the Rails
context.

Refs #18305.

1 files changed, 43 insertions, 3 deletions

diff --git a/guides/source/testing.md b/guides/source/testing.md
index f12daf0dbc..cc469f4dae 100644
--- a/guides/source/testing.md
+++ b/guides/source/testing.md
@@ -407,9 +407,49 @@ This test should now pass.
 
 By now you've caught a glimpse of some of the assertions that are available. Assertions are the worker bees of testing. They are the ones that actually perform the checks to ensure that things are going as planned.
 
-There are a bunch of different types of assertions you can use that come with [`Minitest`](https://github.com/seattlerb/minitest), the default testing library used by Rails.
-
-For a list of all available assertions please check the [Minitest API documentation](http://docs.seattlerb.org/minitest/), specifically [`Minitest::Assertions`](http://docs.seattlerb.org/minitest/Minitest/Assertions.html)
+Here's an extract of the assertions you can use with
+[`Minitest`](https://github.com/seattlerb/minitest), the default testing library
+used by Rails. The `[msg]` parameter is an optional string message you can
+specify to make your test failure messages clearer. It's not required.
+
+| Assertion                                                        | Purpose |
+| ---------------------------------------------------------------- | ------- |
+| `assert( test, [msg] )`                                          | Ensures that `test` is true.|
+| `assert_not( test, [msg] )`                                      | Ensures that `test` is false.|
+| `assert_equal( expected, actual, [msg] )`                        | Ensures that `expected == actual` is true.|
+| `assert_not_equal( expected, actual, [msg] )`                    | Ensures that `expected != actual` is true.|
+| `assert_same( expected, actual, [msg] )`                         | Ensures that `expected.equal?(actual)` is true.|
+| `assert_not_same( expected, actual, [msg] )`                     | Ensures that `expected.equal?(actual)` is false.|
+| `assert_nil( obj, [msg] )`                                       | Ensures that `obj.nil?` is true.|
+| `assert_not_nil( obj, [msg] )`                                   | Ensures that `obj.nil?` is false.|
+| `assert_empty( obj, [msg] )`                                     | Ensures that `obj` is `empty?`.|
+| `assert_not_empty( obj, [msg] )`                                 | Ensures that `obj` is not `empty?`.|
+| `assert_match( regexp, string, [msg] )`                          | Ensures that a string matches the regular expression.|
+| `assert_no_match( regexp, string, [msg] )`                       | Ensures that a string doesn't match the regular expression.|
+| `assert_includes( collection, obj, [msg] )`                      | Ensures that `obj` is in `collection`.|
+| `assert_not_includes( collection, obj, [msg] )`                  | Ensures that `obj` is not in `collection`.|
+| `assert_in_delta( expecting, actual, [delta], [msg] )`           | Ensures that the numbers `expected` and `actual` are within `delta` of each other.|
+| `assert_not_in_delta( expecting, actual, [delta], [msg] )`       | Ensures that the numbers `expected` and `actual` are not within `delta` of each other.|
+| `assert_throws( symbol, [msg] ) { block }`                       | Ensures that the given block throws the symbol.|
+| `assert_raises( exception1, exception2, ... ) { block }`         | Ensures that the given block raises one of the given exceptions.|
+| `assert_nothing_raised( exception1, exception2, ... ) { block }` | Ensures that the given block doesn't raise one of the given exceptions.|
+| `assert_instance_of( class, obj, [msg] )`                        | Ensures that `obj` is an instance of `class`.|
+| `assert_not_instance_of( class, obj, [msg] )`                    | Ensures that `obj` is not an instance of `class`.|
+| `assert_kind_of( class, obj, [msg] )`                            | Ensures that `obj` is or descends from `class`.|
+| `assert_not_kind_of( class, obj, [msg] )`                        | Ensures that `obj` is not an instance of `class` and is not descending from it.|
+| `assert_respond_to( obj, symbol, [msg] )`                        | Ensures that `obj` responds to `symbol`.|
+| `assert_not_respond_to( obj, symbol, [msg] )`                    | Ensures that `obj` does not respond to `symbol`.|
+| `assert_operator( obj1, operator, [obj2], [msg] )`               | Ensures that `obj1.operator(obj2)` is true.|
+| `assert_not_operator( obj1, operator, [obj2], [msg] )`           | Ensures that `obj1.operator(obj2)` is false.|
+| `assert_predicate ( obj, predicate, [msg] )`                     | Ensures that `obj.predicate` is true, e.g. `assert_predicate str, :empty?`|
+| `assert_not_predicate ( obj, predicate, [msg] )`                 | Ensures that `obj.predicate` is false, e.g. `assert_not_predicate str, :empty?`|
+| `assert_send( array, [msg] )`                                    | Ensures that executing the method listed in `array[1]` on the object in `array[0]` with the parameters of `array[2 and up]` is true. This one is weird eh?|
+| `flunk( [msg] )`                                                 | Ensures failure. This is useful to explicitly mark a test that isn't finished yet.|
+
+The above are a subset of assertions that minitest supports. For an exhaustive &
+more up-to-date list, please check
+[Minitest API documentation](http://docs.seattlerb.org/minitest/), specifically
+[`Minitest::Assertions`](http://docs.seattlerb.org/minitest/Minitest/Assertions.html)
 
 Because of the modular nature of the testing framework, it is possible to create your own assertions. In fact, that's exactly what Rails does. It includes some specialized assertions to make your life easier.