System.NotSupportedException

What ckuri said. Just to be clear, you need the following line of code before opening the stream (steps 2,3):

System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);

ExcelDataReader - Important note on .NET Core

By default, ExcelDataReader throws a NotSupportedException "No data is available for encoding 1252." on .NET Core.

To fix, add a dependency to the package System.Text.Encoding.CodePages and then add code to register the code page provider during application initialization (f.ex in Startup.cs):

System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);

This is required to parse strings in binary BIFF2-5 Excel documents encoded with DOS-era code pages. These encodings are registered by default in the full .NET Framework, but not on .NET Core.

I see you are using EF core DbContext in your MovieRepository. So instead of using mock, Using EF Core InMemory database will be a great option for you. This will also reduce the complexity.

Write your GetAllTest() method as follows:

[Fact]
public void GetAllTest()
{
        var options = new DbContextOptionsBuilder<MovieDbContext>()
            .UseInMemoryDatabase(databaseName: "MovieListDatabase")
            .Options;

        // Insert seed data into the database using one instance of the context
        using (var context = new MovieDbContext(options))
        {
            context.Movies.Add(new Movie {Id = 1, Title = "Movie 1", YearOfRelease = 2018, Genre = "Action"});
            context.Movies.Add(new Movie {Id = 2, Title = "Movie 2", YearOfRelease = 2018, Genre = "Action"});
            context.Movies.Add(new Movie {Id = 3, Title = "Movie 3", YearOfRelease = 2019, Genre = "Action"});
            context.SaveChanges();
        }

        // Use a clean instance of the context to run the test
        using (var context = new MovieDbContext(options))
        {
            MovieRepository movieRepository = new MovieRepository(context);
            List<Movies> movies == movieRepository.GetAll();

            Assert.Equal(3, movies.Count);
        }
}

Note: Don't forget to install Microsoft.EntityFrameworkCore.InMemory nuget package as follows:

Install-Package Microsoft.EntityFrameworkCore.InMemory

For more details: Testing with InMemory

.NET Core supports only ASCII, ISO-8859-1 and Unicode encodings, whereas .NET Framework supports much more.

However, .NET Core can be extended to support additional encodings like Windows-1252, Shift-JIS, GB2312 by registering the CodePagesEncodingProvider from the System.Text.Encoding.CodePages NuGet package.

After the NuGet package is installed the following steps as described in the documentation for the CodePagesEncodingProvider class must be done to register the provider:

1. Add a reference to the System.Text.Encoding.CodePages.dll assembly to your project.
2. Retrieve a CodePagesEncodingProvider object from the static Instance property.
3. Pass the CodePagesEncodingProvider object to the Encoding.RegisterProvider method.

EncodingProvider registration code example:

Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);

There is a solution at Paul Welter's Weblog - XML Serializable Generic Dictionary

For some reason, the generic Dictionary in .net 2.0 is not XML serializable. The following code snippet is a xml serializable generic dictionary. The dictionary is serialzable by implementing the IXmlSerializable interface.

using System;
using System.Collections.Generic;
using System.Text;
using System.Xml.Serialization;

[XmlRoot("dictionary")]
public class SerializableDictionary<TKey, TValue>
    : Dictionary<TKey, TValue>, IXmlSerializable
{
    public SerializableDictionary() { }
    public SerializableDictionary(IDictionary<TKey, TValue> dictionary) : base(dictionary) { }
    public SerializableDictionary(IDictionary<TKey, TValue> dictionary, IEqualityComparer<TKey> comparer) : base(dictionary, comparer) { }
    public SerializableDictionary(IEqualityComparer<TKey> comparer) : base(comparer) { }
    public SerializableDictionary(int capacity) : base(capacity) { }
    public SerializableDictionary(int capacity, IEqualityComparer<TKey> comparer) : base(capacity, comparer) { }

    #region IXmlSerializable Members
    public System.Xml.Schema.XmlSchema GetSchema()
    {
        return null;
    }

    public void ReadXml(System.Xml.XmlReader reader)
    {
        XmlSerializer keySerializer = new XmlSerializer(typeof(TKey));
        XmlSerializer valueSerializer = new XmlSerializer(typeof(TValue));

        bool wasEmpty = reader.IsEmptyElement;
        reader.Read();

        if (wasEmpty)
            return;

        while (reader.NodeType != System.Xml.XmlNodeType.EndElement)
        {
            reader.ReadStartElement("item");

            reader.ReadStartElement("key");
            TKey key = (TKey)keySerializer.Deserialize(reader);
            reader.ReadEndElement();

            reader.ReadStartElement("value");
            TValue value = (TValue)valueSerializer.Deserialize(reader);
            reader.ReadEndElement();

            this.Add(key, value);

            reader.ReadEndElement();
            reader.MoveToContent();
        }
        reader.ReadEndElement();
    }

    public void WriteXml(System.Xml.XmlWriter writer)
    {
        XmlSerializer keySerializer = new XmlSerializer(typeof(TKey));
        XmlSerializer valueSerializer = new XmlSerializer(typeof(TValue));

        foreach (TKey key in this.Keys)
        {
            writer.WriteStartElement("item");

            writer.WriteStartElement("key");
            keySerializer.Serialize(writer, key);
            writer.WriteEndElement();

            writer.WriteStartElement("value");
            TValue value = this[key];
            valueSerializer.Serialize(writer, value);
            writer.WriteEndElement();

            writer.WriteEndElement();
        }
    }
    #endregion
}