Create Snapshot

In the inital Testrun Polaroider takes a snapshot of the given object and saves this.
In all further runs Polaroider takes a new snapshot and compares this new snapshot with the saved snapshot.
If the snapshots are not equal, Polaroider throws an AssertionException.

public class MyClass
{
    [Nunit.Framwork.Test]
    public void TestSomething()
    {
        "This is a test snapshot".MatchSnapshot();
    }
}

Polaroider automaticaly saves the Snapshots to the folder _Snapshots. Snapshotfiles are named after the class and the method that the snapshot was taken in.

Snapshots can be created of any object.
The objects internals are mapped to the snapshot by property and value.
Inside the snapshot, hirarchie is displayed by indentation

var obj = new {
    id = 1,
    value = new {
        name = "test"
    }
}

obj.MatchSnapshot();

The generated snapshot looks the following:

id: 1
value:
  name: test

Update Snapshot

The simplest way to update a Snapshot is to delete the Sanpshot file from the folder _Snapshots. Run the test again and the Snapshot is recreated. Alternatively just add the UpdateSnapshotAttribute on the Method

public class MyClass
{
    [Nunit.Framwork.Test]
    [UpdateSnapshot]
    public void TestSomething()
    {
        "This is a test snapshot".MatchSnapshot();
    }
}

Adding the UpdateSnapshotAttribute on the class updates all snapshots of the class

[UpdateSnapshot]
public class MyClass
{
    [Nunit.Framwork.Test]
    public void TestSomething()
    {
        "This is a test snapshot".MatchSnapshot();
    }
}

Multiple Snapshots per test

Snapshots are saved by Class- and Methodname. If it is needed to save multiple Snapshots in a test, just provide some metadata with the snapshot. The snapshots can then be identified by that metadata.

public class MyClass
{
    [Nunit.Framwork.Test]
    public void TestSomething()
    {
        "This is a test snapshot".MatchSnapshot(() => new { id = "one"});

        "This is another test snapshot".MatchSnapshot(() => new { id = "two"});
    }
}

Identitfy Snapshot by metadata

Snapshots can contain metadata. The snapshot is compared with the saved snapshot that contains the same metadata. It is not needed to provide all metadata contained on the saved snapshot, only the data needed to identify the saved snapshot.

The following code matches the snapshot that contains the Key “id” with the value “one” in the metadata

public class MyClass
{
    [Nunit.Framwork.Test]
    public void TestSomething()
    {
        "This is a test snapshot".MatchSnapshot(() => new { id = "one"});
    }
}