Steps to reproduce

'42' | Test-Json | Should -BeTrue
'[ 1, 2 ]' | Test-Json | Should -BeTrue

Expected behavior

The tests should succeed, given that these are valid JSON strings and that piping them to ConvertFrom-Json works just fine:

# These tests pass.
'42' | ConvertFrom-Json | Should -Be 42
'[ 1, 2 ]' | ConvertFrom-Json | Should -Be 1, 2

Actual behavior

Both tests fail.

Environment data

PowerShell Core 7.0.0-rc.1