gnu: Add ephemeralpg.

This is a general utility, but I'm particularly interested in using this to
enable build time tests for the guix-data-service package.

* gnu/packages/databases.scm (ephemeralpg): New variable.

gnu/packages/databases.scm

@@ -216,6 +216,68 @@ (define-public go-gopkg.in-mgo.v2
     (home-page "http://labix.org/mgo")
     (license license:bsd-2)))
 
+(define-public ephemeralpg
+  (package
+    (name "ephemeralpg")
+    (version "2.8")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (string-append
+             "http://eradman.com/ephemeralpg/code/ephemeralpg-"
+             version ".tar.gz"))
+       (sha256
+        (base32 "1dpfxsd8a52psx3zlfbqkw53m35w28qwyb87a8anz143x6gnkkr4"))))
+    (build-system gnu-build-system)
+    (arguments
+     '(#:make-flags (list "CC=gcc"
+                          (string-append "PREFIX=" %output))
+       #:phases
+       (modify-phases %standard-phases
+         (delete 'configure)
+         (replace 'check
+           (lambda* (#:key inputs #:allow-other-keys)
+             ;; The intention for one test is to test without PostgreSQL on
+             ;; the $PATH, so replace the test $PATH with just the util-linux
+             ;; bin, which contains getopt. It will hopefully be possible to
+             ;; remove this for releases after 2.8.
+             (substitute* "test.rb"
+               (("/bin:/usr/bin")
+                (string-append (assoc-ref inputs "util-linux")
+                               "/bin")))
+             ;; Set the LC_ALL=C as some tests use sort, and the locale
+             ;; affects the order. It will hopefully be possible to remove
+             ;; this for releases after 2.8.
+             (setenv "LC_ALL" "C")
+             (invoke "ruby" "test.rb")
+             #t))
+         (add-after 'install 'wrap
+           (lambda* (#:key inputs outputs #:allow-other-keys)
+             (let ((out (assoc-ref outputs "out")))
+               (wrap-program (string-append out "/bin/pg_tmp")
+                 `("PATH" ":" prefix
+                   (,(string-append (assoc-ref inputs "util-linux")
+                                    "/bin")
+                    ,(string-append (assoc-ref inputs "postgresql")
+                                    "/bin")
+                    ;; For getsocket
+                    ,(string-append out "/bin")))))
+             #t)))))
+    (inputs
+     `(("postgresql" ,postgresql)
+       ("util-linux" ,util-linux)))
+    (native-inputs
+     `(("ruby" ,ruby)))
+    (home-page "http://eradman.com/ephemeralpg/")
+    (synopsis "Run temporary PostgreSQL databases")
+    (description
+     "@code{pg_tmp} creates temporary PostgreSQL databases, suitable for tasks
+like running software test suites.  Temporary databases created with
+@code{pg_tmp} have a limited shared memory footprint and are automatically
+garbage-collected after a configurable number of seconds (the default is
+60).")
+    (license license:isc)))
+
 (define-public es-dump-restore
   (package
     (name "es-dump-restore")