Repository: scikit-learn/scikit-learn
Issue category: Bug Report

Issue:
Missing format string arguments
This assertion error string is not properly formatted as the 2 format arguments `y_pred.shape` and `y.shape` are missing:

https://github.com/scikit-learn/scikit-learn/blob/551d56c254197c4b6ad63974d749824ed2c7bc58/sklearn/utils/estimator_checks.py#L2139

```python
assert y_pred.shape == y.shape, (
    "The shape of the prediction for multioutput data is incorrect."
    " Expected {}, got {}."
)
```

should become

```python
assert y_pred.shape == y.shape, (
    "The shape of the prediction for multioutput data is incorrect."
    " Expected {}, got {}.".format(y_pred.shape, y.shape)
)
```


Hints:
Please feel free to directly submit a PR with the fix in the future in such cases :) 

Patch:
diff --git a/sklearn/utils/estimator_checks.py b/sklearn/utils/estimator_checks.py
index f5d542d9a59fc..da1300817b148 100644
--- a/sklearn/utils/estimator_checks.py
+++ b/sklearn/utils/estimator_checks.py
@@ -2076,11 +2076,11 @@ def check_regressor_multioutput(name, estimator):
 
     assert y_pred.dtype == np.dtype("float64"), (
         "Multioutput predictions by a regressor are expected to be"
-        " floating-point precision. Got {} instead".format(y_pred.dtype)
+        f" floating-point precision. Got {y_pred.dtype} instead"
     )
     assert y_pred.shape == y.shape, (
         "The shape of the prediction for multioutput data is incorrect."
-        " Expected {}, got {}."
+        f" Expected {y_pred.shape}, got {y.shape}."
     )
 
 


Test patch: