Prefer Minitest's location for test failures.

When running tests, the Rails test runner would report the start of the test method as the test failure.

For this test:

```ruby
1 require 'test_helper
2
3 class BunnyTest < ActiveSupport::TestCase
4   test "something failing" do
5     assert false, 'This failed'
6   end
7 end
```

The runner outputs 5 instead of 4:

```
............................................F

This failed

bin/rails test test/models/bunny_test.rb:5

........
```

1 files changed, 8 insertions, 2 deletions

diff --git a/railties/lib/rails/test_unit/reporter.rb b/railties/lib/rails/test_unit/reporter.rb
index e1fe92a11b..de4b002e55 100644
--- a/railties/lib/rails/test_unit/reporter.rb
+++ b/railties/lib/rails/test_unit/reporter.rb
@@ -57,8 +57,14 @@ module Rails
       end
 
       def format_rerun_snippet(result)
-        location, line = result.method(result.name).source_location
-        "#{self.executable} #{relative_path_for(location)}:#{line}"
+        # Try to extract path to assertion from backtrace.
+        if result.location =~ /\[(.*)\]\z/
+          assertion_path = $1
+        else
+          assertion_path = result.method(result.name).source_location.join(':')
+        end
+
+        "#{self.executable} #{relative_path_for(assertion_path)}"
       end
   end
 end