Help expanding tester

It looks like the error is caused by the attempt to expand the Tester record in the OData feed. According to the error message, the Analytics Service doesn't support key or property navigation like "WorkItems(Id)" or "WorkItem(Id)/AssignedTo".

One way to resolve this issue is to try to avoid expanding the Tester record in the query. Instead, you can retrieve the Tester ID and use it to join with another table that contains the Tester's User Name. Here's an example query that shows how to do this:

let
Source = OData.Feed("https://analytics.dev.azure.com/mycompany/myproject/_odata/v3.0-preview/TestPoints?" & "$apply=filter((TestSuite/TestPlanTitle eq 'MyTopLevelTestPlan' and TestSuite/IdLevel2 ne null and TestSuite/IdLevel3 ne null))"),
#"Filtered Rows" = Table.SelectRows(Source, each ([LastResultOutcome] = "Passed")),
#"Extracted Tester ID" = Table.TransformColumns(#"Filtered Rows", {"Tester", each Record.Field(_, "Id")}),
#"Merged with Tester Table" = Table.NestedJoin(#"Extracted Tester ID", {"Tester"}, TesterTable, {"Id"}, "Tester", JoinKind.LeftOuter),
#"Expanded Tester UserName" = Table.ExpandTableColumn(#"Merged with Tester Table", "Tester", {"UserName"}, {"Tester.UserName"})
in
#"Expanded Tester UserName"

In this example, I'm assuming that you have another table called TesterTable that contains the Tester ID and User Name. You can join the TestPoints table with the TesterTable using the Tester ID, and then expand the User Name field from the joined table.