Add Run The Test At A Specific Line Number as an elixir til

elixir/run-the-test-at-a-specific-line-number.md

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+# Run The Test At A Specific Line Number
+
+You can tell `mix test` to only run tests that appear in a specific file by
+naming the file:
+
+```bash
+$ mix test test/module/file_test.exs
+```
+
+You can even point it to a specific line number in that file like so:
+
+```bash
+$ mix test test/module/file_test.exs:45
+```
+
+Behind the scenes, `mix test` is using tags to build a list of exclusions
+and inclusions that result in only the test at line 45 running. Here is an
+equivalent of the above command:
+
+```bash
+$ mix test test/module/file_test.exs --exclude test --include line:45
+```
+
+This will exclude every test. It will then re-include the test that
+corresponds to having a tag `line:45`.