Can you please confirm whether the #53698 fixes this?
The only way I could reproduce the failure was by explicitly setting the AWS_REGION env var before running the test.

@marcoandredinis I also suspected that the region var plays a role here, but I don't have it set at all - and your proposed fix doesn't work in my case.

I'm attaching a test log, if that helps. test-log.txt

Also: running the test with AWS_REGION set doesn't change anything.

No issues for me:

 ➜ go test ./lib/integrations/awsoidc -run TestNewIdPIAMConfigureClient -count=100
ok      github.com/gravitational/teleport/lib/integrations/awsoidc      1.050s

I was able to reproduce a failure by setting the env var

marcodinis@MarcoM3 ~/s/teleport (master)> go test -run TestNewIdPIAMConfigureClient github.com/gravitational/teleport/lib/integrations/awsoidc -count 1
ok      github.com/gravitational/teleport/lib/integrations/awsoidc      1.018s
marcodinis@MarcoM3 ~/s/teleport (master)> AWS_REGION=abcd go test -run TestNewIdPIAMConfigureClient github.com/gravitational/teleport/lib/integrations/awsoidc -coun
t 1
--- FAIL: TestNewIdPIAMConfigureClient (0.00s)
    --- FAIL: TestNewIdPIAMConfigureClient/no_aws_region_env_var,_returns_an_error (0.00s)
        idp_iam_config_test.go:562: 
                Error Trace:    /Users/marcodinis/src/teleport/lib/integrations/awsoidc/idp_iam_config_test.go:562
                Error:          An error is expected but got nil.
                Test:           TestNewIdPIAMConfigureClient/no_aws_region_env_var,_returns_an_error
FAIL
FAIL    github.com/gravitational/teleport/lib/integrations/awsoidc      1.025s
FAIL

Hence, my fix. But it might be something else.

Can you please check your env | grep AWS_ and your ~/.aws/config ? They might be setting a region (eg there's AWS_REGION and AWS_DEFAULT_REGION).

@marcoandredinis Indeed, I investigated the environment variable, but forgot about the config file itself. Removing the default profile helped. The question remains whether this should or should not influence this unit test, so up to you whether to close this issue or fix it. Thanks!

I'll try to merge #53698 because I still see value in that PR even if it doesn't fix the root cause of your use case.

I'm fine leaving this as is for now.
I have mixed feelings about checking the contents of ~/.aws/config or whatever file $AWS_CONFIG_FILE points to.