Format-Table returns null when run on vsts. The possible reason is that it tries to adjust table to the console dimensions and some parameters of the console like e.g. width might not be set on vsts. In this case the width of the Format-Table results should be set to some default value e.g. 80.

The workaround for that is using Out-String -Width e.g.:
$result = Format-Table -inputobject @{'test'= 1, 2} | Out-String -Width 80

But the expected behavior is that Format-Table returns non null results regardless of the environment.

Steps to reproduce

$result = Format-Table -inputobject @{'test'= 1, 2}

Expected behavior

Name                           Value
----                           -----
test                           {1, 2}

Actual behavior

$result is null

Environment data

> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      6.1.0-preview.1
PSEdition                      Core
GitCommitId                    v6.1.0-preview.1
OS                             Linux 4.9.87-linuxkit-aufs #1 SMP Wed Mar 14 15:12:16 UTC 2018
Platform                       Unix
PSCompatibleVersions           {...}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0