[BUG] AsyncPageable.FromPages doesn't return a pageable object

[cyrildurand]

For one of my test I'm trying to mock an AsyncPageable object. I use the FromPages, AsPages and FromValues methods.

I read this article that explain mocking and asyncpageable but multi page is not mentionned.

My code is similar to this :

    var page1 = new List<String>() { "A", "B" };
    var page2 = new List<String>() { "C", "D" };

    var pages = AsyncPageable<String>.FromPages(new[] {
        Page<String>.FromValues(page1, "X", Mock.Of<Response>()),
        Page<String>.FromValues(page2, null, Mock.Of<Response>())
    });

When I'm requesting the first page, without a continuationToken value

    var q = pages.AsPages(continuationToken: null);
    var currentPage = await q.FirstOrDefaultAsync();

currentPage contains 2 elements (A, B) and the continuationToken is set to X.

When I'm requesting for the second page, with a continuationToken of X

    var q = pages.AsPages(continuationToken: "X");
    var currentPage = await q.FirstOrDefaultAsync();

currentPage is still the first page and not the second page.

Expected behavior

When we query for another page with a valid continuationToken we obtain the corresponding page and not the first page.

Actual behavior (include Exception or Stack Trace)

The issue only happens when I'm using mocking an AsyncPageable with FromPages. When I'm requesting data from CosmosDb everything works normally.

The issue seems to come from Pageable.cs#L127. FromPages returns a StaticPageable and then in the AsPages method The continuationToken is ignored.

        public override IEnumerable<Page<T>> AsPages(string? continuationToken = default, int? pageSizeHint = default)
        {
            return _pages;
        }

To Reproduce

    [Fact]
    public async Task AsyncPageableTest()
    {
        var page1 = new List<String>() { "A", "B" };
        var page2 = new List<String>() { "C", "D" };

        var pages = AsyncPageable<String>.FromPages(new[] {
            Page<String>.FromValues(page1, "X", Mock.Of<Response>()),
            Page<String>.FromValues(page2, null, Mock.Of<Response>())
        });

        // test first page : OK
        var q = pages.AsPages(continuationToken: null);
        var currentPage = await q.FirstOrDefaultAsync();

        Assert.Collection(currentPage.Values,
            o => Assert.Equal("A", o),
            o => Assert.Equal("B", o)
        );
        Assert.Equal("X", currentPage.ContinuationToken);


        // test second page : KO
        q = pages.AsPages(continuationToken: "X");
        currentPage = await q.FirstOrDefaultAsync();

        Assert.Collection(currentPage.Values,
            o => Assert.Equal("C", o),
            o => Assert.Equal("D", o)
        );
        Assert.Null(currentPage.ContinuationToken);
    }

Environment:

• Name and version of the Library package used: Azure.Core 1.8.1.0
• Hosting platform or OS and .NET runtime version (dotnet --info output for .NET Core projects):

PS C:\XXX> dotnet --info
.NET SDK (reflecting any global.json):
 Version:   5.0.205
 Commit:    64a0cf25eb

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19043
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\5.0.205\

Host (useful for support):
  Version: 5.0.8
  Commit:  35964c9215

.NET SDKs installed:
  3.1.411 [C:\Program Files\dotnet\sdk]
  5.0.203 [C:\Program Files\dotnet\sdk]
  5.0.205 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.All 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]  
  Microsoft.WindowsDesktop.App 3.1.17 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]  
  Microsoft.WindowsDesktop.App 5.0.6 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]   
  Microsoft.WindowsDesktop.App 5.0.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]   

• IDE and version : Visual Studio 16.9.6

[jsquire]

Thank you for your feedback. Tagging and routing to the team member best able to assist.