UseDefaultTag for skip build if not default branch.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

docker_test.go

@@ -0,0 +1,25 @@
+package docker
+
+import "testing"
+
+func Test_stripHeadPrefix(t *testing.T) {
+	type args struct {
+		ref string
+	}
+	tests := []struct {
+		args args
+		want string
+	}{
+		{
+			args: args{
+				ref: "refs/heads/master",
+			},
+			want: "master",
+		},
+	}
+	for _, tt := range tests {
+		if got := stripHeadPrefix(tt.args.ref); got != tt.want {
+			t.Errorf("stripHeadPrefix() = %v, want %v", got, tt.want)
+		}
+	}
+}