feat(schema): testing utilities (#20705)

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

schema/testing/appdatasim/diff_test.go

@@ -0,0 +1,39 @@
+package appdatasim
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"gotest.tools/v3/golden"
+
+	"cosmossdk.io/schema"
+	schematesting "cosmossdk.io/schema/testing"
+)
+
+// this test checks that diffs in app data are deterministic and can be used for regression testing
+func TestDiffAppData(t *testing.T) {
+	appSim, err := NewSimulator(Options{
+		AppSchema: schematesting.ExampleAppSchema,
+	})
+	require.NoError(t, err)
+
+	mirror, err := NewSimulator(Options{
+		// add just one module to the mirror
+		AppSchema: map[string]schema.ModuleSchema{
+			"all_kinds": schematesting.ExampleAppSchema["all_kinds"],
+		},
+	})
+	require.NoError(t, err)
+
+	// mirror one block
+	blockGen := appSim.BlockDataGenN(50, 100)
+	blockData := blockGen.Example(1)
+	require.NoError(t, appSim.ProcessBlockData(blockData))
+	require.NoError(t, mirror.ProcessBlockData(blockData))
+
+	// produce another block, but don't mirror it so that they're out of sync
+	blockData = blockGen.Example(2)
+	require.NoError(t, appSim.ProcessBlockData(blockData))
+
+	golden.Assert(t, DiffAppData(appSim, mirror), "diff_example.txt")
+}