Initialize Steps with a NewSTEPNAME function [#67]

This seems to be be a more natural separation of concerns--the knowledge
of which config fields map to which parts of a Step belong to the Step,
not to the Plan.

internal/run/addrepo_test.go

@@ -38,6 +38,12 @@ func TestAddRepoTestSuite(t *testing.T) {
 	suite.Run(t, new(AddRepoTestSuite))
 }
 
+func (suite *AddRepoTestSuite) TestNewAddRepo() {
+	repo := NewAddRepo("picompress=https://github.com/caleb_phipps/picompress")
+	suite.Require().NotNil(repo)
+	suite.Equal("picompress=https://github.com/caleb_phipps/picompress", repo.Repo)
+}
+
 func (suite *AddRepoTestSuite) TestPrepareAndExecute() {
 	stdout := strings.Builder{}
 	stderr := strings.Builder{}