Test-Json doesn't recognize JSON arrays or primitives

[mklement0]

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

[iSazonov]

@mklement0 Could you please add more info why it should work in the way? Maybe reference to a standard or a quote from the standard. It would help to avoid regressions in follow fix.

[mklement0]

@iSazonov, I've added a link to json.org to the OP, and also a demonstration that ConvertFrom-Json itself happily accepts such inputs.

[iSazonov]

We use NewtonSoft JObject.Parse() which throws. I tried System.Text.Json.JsonDocument.Parse() and … most of our tests failed because examples in the issue and out tests in Test-Json.Tests.ps1 use single quotes but Json standard allows only double quotes.
So we should decide what to do because switching to JsonDocument.Parse() looks like a breaking change.
With double quotes the tests and the issue examples are passed if JsonDocument.Parse() is used.

[mklement0]

use single quotes but Json standard allows only double quotes.

The single quotes aren't in the data, they are only there as PowerShell's string delimiter.

What Test-Json sees is just 42 and [ 1, 2 ] and both are valid JSON strings.

I haven't looked at the internals, but it's obvious that whatever ConvertFrom-Json manages to parse should be considered valid by Test-Json.

[jochenvanwylick]

+1 Encountered the same problem here - would love to see this resolved!

[iSazonov]

@jochenvanwylick You could download artifact from #11397, check your scenarios and report issues there.

[mklement0]

@iSazonov: In the current implementation,

PowerShell/src/Microsoft.PowerShell.Commands.Utility/commands/utility/TestJsonCommand.cs

Line 70 in 7b33cfe

parsedJson = JObject.Parse(Json);

should be:

parsedJson = JToken.Parse(Json);

Only JToken correctly parses JSON documents such as 42 and [ 1, 2 ], whereas JObject accepts just a single object (dictionary).

Or, better yet, use the same technique that ConvertFrom-Json uses:

PowerShell/src/Microsoft.PowerShell.Commands.Utility/commands/utility/WebCmdlet/JsonObject.cs

Lines 179 to 187 in 7b33cfe

	var obj = JsonConvert.DeserializeObject(
	input,
	new JsonSerializerSettings
	{
	// This TypeNameHandling setting is required to be secure.
	TypeNameHandling = TypeNameHandling.None,
	MetadataPropertyHandling = MetadataPropertyHandling.Ignore,
	MaxDepth = maxDepth
	});

Note that the code there contains a workaround for a NewtonSoft bug that's no longer needed.

---

In a System.Text.Json-based implementation, System.Text.Json.JsonDocument.Parse() is indeed the right tool.

---

All these tests succeed:

# Valid JSON
'42', '[ 1, 2 ]', '{ "foo": 1 }' | % {
    {  [System.Text.Json.JsonDocument]::Parse($_) } | Should -Not -Throw
    {  [Newtonsoft.Json.Linq.JToken]::Parse($_)  } | Should -Not -Throw
}

# Invalid JSON
'a', '[', '{ "foo": 1 }, { "bar": 2 }' | % {
    {  [System.Text.Json.JsonDocument]::Parse($_) } | Should -Throw
    {  [Newtonsoft.Json.Linq.JToken]::Parse($_)  } | Should -Throw
}

[iSazonov]

@mklement0 Thanks! I think we should move to Core API if possible. Sooner or later it will happen anyway. If there are no serious problems, it is better to do it "sooner".

[thedavecarroll]

Has there been any progress on this?

A Redditor recently made a similar comment. I responded with a link to this issue.

Basically, I said that they could use ConvertFrom-Json | ConvertTo-Json | Test-Json to perform tests.

'[ { name : "Joe" } ]' | ConvertFrom-Json | ConvertTo-Json | Test-Json

Is this the best advice for PowerShell 7 GA?

[mklement0]

@thedavecarroll, yes, it's unfortunate that this wasn't addressed in time for 7.0

PR #11397 will implicitly fix these issues, if I understand correctly, but due to its move to a different underlying API it will bring breaking changes, notably no longer being able to use single-quoted JSON (right, @iSazonov?).

I wasn't even aware of the other issue that Test-Json doesn't support its input as an array of lines, the way ConvertFrom-Json does (e.g., '{ "foo": ', '"bar" }' | Test-Json fails, which succeeds with ConvertFrom-Json)

As for a workaround: It's sufficient to use only ConvertFrom-Json, and derive from its failure whether the input is valid JSON or not:

$valid = try { $null = '[ { name : "Joe" } ]' | ConvertFrom-Json; $true } catch { $false }

[iSazonov]

@mklement0 Yes.
Currently we are waiting .Net 5.0 public preview to continue.

[dgard1981]

Might we get another update on this issue?

@iSazonov said -

Currently we are waiting .Net 5.0 public preview to continue.

Looks like this has now happened.

With regards to suggested workarounds using ConvertFrom-Json - unfortunately that's no good if you are trying to test against a schema.