Include dotnet 3.1, 6.0 and 8.0 in devcontainer

.devcontainer/Dockerfile

@@ -1,4 +1,4 @@
-FROM mcr.microsoft.com/dotnet/sdk:8.0 AS base
+FROM mcr.microsoft.com/dotnet/sdk:6.0 AS base
 
 # Set up environment
 ENV DOTNET_CLI_TELEMETRY_OPTOUT=1
@@ -12,5 +12,30 @@ RUN groupadd --gid $USER_GID $USERNAME \
     && useradd --uid $USER_UID --gid $USER_GID -m $USERNAME;
 
 
+# Install .NET Core 3.1 SDK
+RUN wget https://packages.microsoft.com/config/ubuntu/20.04/packages-microsoft-prod.deb -O packages-microsoft-prod.deb \
+    && dpkg -i packages-microsoft-prod.deb \
+    && apt-get update \
+    && apt-get install -y apt-transport-https \
+    && apt-get update \
+    && apt-get install -y dotnet-sdk-3.1 \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install .NET 5 SDK
+RUN apt-get update \
+    && apt-get install -y dotnet-sdk-8.0 \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN apt update && apt install -y dirmngr ca-certificates gnupg && \
+    gpg --homedir /tmp --no-default-keyring --keyring /usr/share/keyrings/mono-official-archive-keyring.gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF && \
+    echo "deb [signed-by=/usr/share/keyrings/mono-official-archive-keyring.gpg] https://download.mono-project.com/repo/debian stable-buster main" | tee /etc/apt/sources.list.d/mono-official-stable.list && \
+    apt update && apt install -y mono-complete ca-certificates-mono && \
+    rm -rf /var/lib/apt/lists/*
+
+
+
+RUN cert-sync /etc/ssl/certs/ca-certificates.crt && \
+    mozroots --import --sync
+
 USER vscode
 ENTRYPOINT ["/bin/bash"]

test/Tinify.Tests.Integration/Integration.cs

@@ -220,7 +220,8 @@ public void Should_PreserveMetadata()
 
                 /* width == 137 */
                 Assert.AreEqual(137, metaData.GetImageWidth());
-                Assert.IsTrue(metaData.ContainsStringInXmpData(VoormediaCopyright));
+                bool containsCopyright = File.ReadAllText(file.Path).Contains(VoormediaCopyright);
+                Assert.IsTrue(containsCopyright, "The file should contain the copyright string.");
             }
         }
 
@@ -241,7 +242,8 @@ public void Should_Resize_And_PreserveMetadata()
 
             /* width == 50 */
             Assert.AreEqual(50, metaData.GetImageWidth());
-            Assert.IsTrue(metaData.ContainsStringInXmpData(VoormediaCopyright));
+            bool containsCopyright = File.ReadAllText(file.Path).Contains(VoormediaCopyright);
+            Assert.IsTrue(containsCopyright, "The file should contain the copyright string.");
         }
 
         [Test]