Add elisp/two-fer

elisp/two-fer/README.md

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+# Two Fer
+
+`Two-fer` or `2-fer` is short for two for one. One for you and one for me.
+
+```text
+"One for X, one for me."
+```
+
+When X is a name or "you".
+
+If the given name is "Alice", the result should be "One for Alice, one for me."
+If no name is given, the result should be "One for you, one for me."
+
+## Source
+
+[https://en.wikipedia.org/wiki/Two-fer](https://en.wikipedia.org/wiki/Two-fer)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

elisp/two-fer/two-fer-test.el

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+;;; two-fer-test.el --- Tests for Two-fer (exercism)
+
+;;; Commentary:
+;; Common test data version: 1.2.0 4fc1acb
+
+;;; Code:
+
+(load-file "two-fer.el")
+
+(ert-deftest no-name-given ()
+  (should (equal (two-fer) "One for you, one for me.")))
+
+(ert-deftest a-name-given ()
+  (should (equal (two-fer "Alice") "One for Alice, one for me.")))
+
+(ert-deftest another-name-given ()
+  (should (equal (two-fer "Bob") "One for Bob, one for me.")))
+
+(provide 'two-fer-test)
+
+;;; two-fer-test.el ends here

elisp/two-fer/two-fer.el

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+;;; two-fer.el --- Two-fer Exercise (exercism)
+
+;;; Commentary:
+
+;;; Code:
+
+(provide 'two-fer)
+
+(defun two-fer(&optional name)
+  "Return a twofer phrase as a formatted string.
+NAME, if provided, is used to specify the first recipient;
+it defaults to 'you'."
+  (if (not name) (setq name "you"))
+  (format "One for %s, one for me." name))
+;;; two-fer.el ends here