unit8co/darts

Improve error message when future covariates are missing during backtest() call

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#2,846 opened on Jul 18, 2025

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good first issueimprovement

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Description

Is your feature request related to a current problem? Please describe. Yes.When using backtest() with a model trained with train and val future covariates, forgetting to pass the full future covariates again at backtest time results in an error (IndexError: index 1 is out of bounds for axis 0 with size 1.).

Describe proposed solution A better explanation or error message should be thrown as it is the case for "regular" historical forecasts.

Additional context Error currently thrown :

IndexError: index 1 is out of bounds for axis 0 with size 1.

Contributor guide

Research direction
Locate the backtest() method in the codebase. Identify where the IndexError is raised when future covariates are missing. Add a check to detect the missing covariates and raise a descriptive error message instead.
Tech stack
python
Domain
datamachine learning
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
PythonGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75