diff --git a/src/EditorFeatures/VisualBasicTest/SimplifyInterpolation/SimplifyInterpolationTests.vb b/src/EditorFeatures/VisualBasicTest/SimplifyInterpolation/SimplifyInterpolationTests.vb
new file mode 100644
index 0000000000000000000000000000000000000000..9b78a94aa02ea99ad2eefb1afd9ad5f25413bd1c
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+++ b/src/EditorFeatures/VisualBasicTest/SimplifyInterpolation/SimplifyInterpolationTests.vb
@@ -0,0 +1,516 @@
+' Licensed to the .NET Foundation under one or more agreements.
+' The .NET Foundation licenses this file to you under the MIT license.
+' See the LICENSE file in the project root for more information.
+
+Imports Microsoft.CodeAnalysis.CodeFixes
+Imports Microsoft.CodeAnalysis.Diagnostics
+Imports Microsoft.CodeAnalysis.Editor.VisualBasic.UnitTests.Diagnostics
+Imports Microsoft.CodeAnalysis.VisualBasic.SimplifyInterpolation
+
+Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.UnitTests.SimplifyInterpolation
+    <Trait(Traits.Feature, Traits.Features.CodeActionsSimplifyInterpolation)>
+    Public Class SimplifyInterpolationTests
+        Inherits AbstractVisualBasicDiagnosticProviderBasedUserDiagnosticTest
+
+        Friend Overrides Function CreateDiagnosticProviderAndFixer(workspace As Workspace) As (DiagnosticAnalyzer, CodeFixProvider)
+            Return (New VisualBasicSimplifyInterpolationDiagnosticAnalyzer(),
+                    New VisualBasicSimplifyInterpolationCodeFixProvider())
+        End Function
+
+        <Fact>
+        Public Async Function SubsequentUnnecessarySpansDoNotRepeatTheSmartTag() As Task
+            Dim parameters = New TestParameters(retainNonFixableDiagnostics:=True, includeDiagnosticsOutsideSelection:=True)
+
+            Using workspace = CreateWorkspaceFromOptions("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue{|Unnecessary:[||].ToString()|}{|Unnecessary:.PadLeft(|}{|Unnecessary:3|})} suffix""
+    End Sub
+End Class", parameters)
+
+                Dim diagnostics = Await GetDiagnosticsWorkerAsync(workspace, parameters)
+
+                Assert.Equal(
+                    {
+                        ("IDE0071", DiagnosticSeverity.Info),
+                        ("IDE0071WithoutSuggestion", DiagnosticSeverity.Hidden),
+                        ("IDE0071WithoutSuggestion", DiagnosticSeverity.Hidden)
+                    },
+                    diagnostics.Select(Function(d) (d.Descriptor.Id, d.Severity)))
+            End Using
+        End Function
+
+        <Fact>
+        Public Async Function ToStringWithNoParameter() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue{|Unnecessary:[||].ToString()|}} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function ToStringWithParameter() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue{|Unnecessary:[||].ToString(""|}g{|Unnecessary:"")|}} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue:g} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function ToStringWithEscapeSequences() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue{|Unnecessary:[||].ToString(""|}""""d""""{|Unnecessary:"")|}} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue:""""d""""} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function ToStringWithStringConstantParameter() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Const someConst As String = ""some format code""
+        Dim v = $""prefix {someValue[||].ToString(someConst)} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function ToStringWithCharacterLiteralParameter() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As C)
+        Dim v = $""prefix {someValue[||].ToString(""f""c)} suffix""
+    End Sub
+
+    Function ToString(_ As Object) As String
+        Return ""Goobar""
+    End Function
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function ToStringWithFormatProvider() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].ToString(""some format code"", System.Globalization.CultureInfo.CurrentCulture)} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadLeftWithIntegerLiteral() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue{|Unnecessary:[||].PadLeft(|}3{|Unnecessary:)|}} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue,3} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadRightWithIntegerLiteral() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue{|Unnecessary:[||].PadRight(|}3{|Unnecessary:)|}} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue,-3} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadLeftWithComplexConstantExpression() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Const someConstant As Integer = 1
+        Dim v = $""prefix {someValue{|Unnecessary:[||].PadLeft(|}CByte(3.3) + someConstant{|Unnecessary:)|}} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Const someConstant As Integer = 1
+        Dim v = $""prefix {someValue,CByte(3.3) + someConstant} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadLeftWithSpaceChar() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue{|Unnecessary:[||].PadLeft(|}3{|Unnecessary:, "" ""c)|}} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue,3} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadRightWithSpaceChar() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue{|Unnecessary:[||].PadRight(|}3{|Unnecessary:, "" ""c)|}} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue,-3} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadLeftWithNonSpaceChar() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].PadLeft(3, ""x""c)} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadRightWithNonSpaceChar() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].PadRight(3, ""x""c)} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadRightWithComplexConstantExpressionRequiringParentheses() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Const someConstant As Integer = 1
+        Dim v = $""prefix {someValue{|Unnecessary:[||].PadRight(|}CByte(3.3) + someConstant{|Unnecessary:)|}} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Const someConstant As Integer = 1
+        Dim v = $""prefix {someValue,-(CByte(3.3) + someConstant)} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function ToStringWithNoParameterWhenFormattingComponentIsSpecified() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].ToString():goo} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function ToStringWithStringLiteralParameterWhenFormattingComponentIsSpecified() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].ToString(""bar""):goo} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function ToStringWithNoParameterWhenAlignmentComponentIsSpecified() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue{|Unnecessary:[||].ToString()|},3} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue,3} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function ToStringWithNoParameterWhenBothComponentsAreSpecified() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].ToString(),3:goo} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function ToStringWithStringLiteralParameterWhenBothComponentsAreSpecified() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].ToString(""some format code""),3:goo} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadLeftWhenFormattingComponentIsSpecified() As Task
+            Await TestInRegularAndScript1Async("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].PadLeft(3):goo} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue,3:goo} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadRightWhenFormattingComponentIsSpecified() As Task
+            Await TestInRegularAndScript1Async("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].PadRight(3):goo} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue,-3:goo} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadLeftWhenAlignmentComponentIsSpecified() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].PadLeft(3),3} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadRightWhenAlignmentComponentIsSpecified() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].PadRight(3),3} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadLeftWhenBothComponentsAreSpecified() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].PadLeft(3),3:goo} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadRightWhenBothComponentsAreSpecified() As Task
+            Await TestMissingInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue[||].PadRight(3),3:goo} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function ToStringWithoutFormatThenPadLeft() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue{|Unnecessary:[||].ToString()|}{|Unnecessary:.PadLeft(|}3{|Unnecessary:)|}} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue,3} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadLeftThenToStringWithoutFormat() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue.PadLeft(3){|Unnecessary:[||].ToString()|}} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue.PadLeft(3)} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadLeftThenToStringWithoutFormatWhenAlignmentComponentIsSpecified() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue.PadLeft(3){|Unnecessary:[||].ToString()|},3} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue.PadLeft(3),3} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadLeftThenPadRight_WithoutAlignment() As Task
+            Await TestInRegularAndScriptAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue.PadLeft(3){|Unnecessary:[||].PadRight(|}3{|Unnecessary:)|}} suffix""
+    End Sub
+End Class", "
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue.PadLeft(3),-3} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact>
+        Public Async Function PadLeftThenPadRight_WithAlignment() As Task
+            Await TestMissingAsync("
+Class C
+    Sub M(someValue As String)
+        Dim v = $""prefix {someValue.PadLeft(3)[||].PadRight(3),3} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact, WorkItem(41381, "https://github.com/dotnet/roslyn/issues/41381")>
+        Public Async Function MissingOnImplicitToStringReceiver() As Task
+            Await TestMissingAsync("
+Class C
+    Public Overrides Function ToString() As String
+        Return ""Goobar""
+    End Function
+
+    Function GetViaInterpolation() As String
+        Return $""Hello {ToString[||]()}""
+    End Function
+End Class")
+        End Function
+
+        <Fact, WorkItem(41381, "https://github.com/dotnet/roslyn/issues/41381")>
+        Public Async Function MissingOnImplicitToStringReceiverWithArg() As Task
+            Await TestMissingAsync("
+Class C
+    Function ToString(arg As String) As String
+        Return ""Goobar""
+    End Function
+
+    Function GetViaInterpolation() As String
+        Return $""Hello {ToString[||](""g"")}""
+    End Function
+End Class")
+        End Function
+
+        <Fact, WorkItem(41381, "https://github.com/dotnet/roslyn/issues/41381")>
+        Public Async Function MissingOnStaticToStringReceiver() As Task
+            Await TestMissingAsync("
+Class C
+    Shared Function ToString() As String
+        Return ""Goobar""
+    End Function
+
+    Function GetViaInterpolation() As String
+        Return $""Hello {ToString[||]()}""
+    End Function
+End Class")
+        End Function
+
+        <Fact, WorkItem(41381, "https://github.com/dotnet/roslyn/issues/41381")>
+        Public Async Function MissingOnStaticToStringReceiverWithArg() As Task
+            Await TestMissingAsync("
+Class C
+    Shared Function ToString(arg As String) As String
+        Return ""Goobar""
+    End Function
+
+    Function GetViaInterpolation() As String
+        Return $""Hello {ToString[||](""g"")}""
+    End Function
+End Class")
+        End Function
+
+        <Fact, WorkItem(41381, "https://github.com/dotnet/roslyn/issues/41381")>
+        Public Async Function MissingOnImplicitPadLeft() As Task
+            Await TestMissingAsync("
+Class C
+    Function PadLeft(ByVal val As Integer) As String
+        Return """"
+    End Function
+
+    Sub M(someValue As String)
+        Dim v = $""prefix {[||]PadLeft(3)} suffix""
+    End Sub
+End Class")
+        End Function
+
+        <Fact, WorkItem(41381, "https://github.com/dotnet/roslyn/issues/41381")>
+        Public Async Function MissingOnStaticPadLeft() As Task
+            Await TestMissingAsync("
+Class C
+    Shared Function PadLeft(ByVal val As Integer) As String
+        Return """"
+    End Function
+
+    Sub M(someValue As String)
+        Dim v = $""prefix {[||]PadLeft(3)} suffix""
+    End Sub
+End Class")
+        End Function
+    End Class
+End Namespace