Add initial tests for specific logic of git-elegant.bash

The tests handle unknown and non-provided commands. They allow making
some refactoring of git-elegant.bash.

In general, the tests for git-elegant.bash have to cover a logic of
invocation of other commands or some corner cases.

#118

tests/git-elegant.bats

@@ -0,0 +1,15 @@
+#!/usr/bin/env bats
+
+load addons-common
+
+@test "'git elegant': a help is displayed if a command is not provided" {
+    check git-elegant
+    [[ "$status" -eq 0 ]]
+    [ ${#lines[@]} -gt 3 ]
+}
+
+@test "'git elegant': a unknown command is handled in user-friendly way" {
+    check git-elegant sdfsdfsd
+    [[ "$status" -eq 46 ]]
+    [[ "${lines[@]}" =~ "Unknown command: git elegant sdfsdfsd" ]]
+}