test(view): improve test coverage (#7543)

Cover edge cases in config parser. Add rudimentary View/Filter
tests. Improves test coverage from 44% to 82%.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

plugin/view/metadata_test.go

@@ -0,0 +1,22 @@
+package view
+
+import (
+	"context"
+	"testing"
+
+	"github.com/coredns/coredns/plugin/metadata"
+	"github.com/coredns/coredns/request"
+)
+
+func TestMetadata_PublishesViewName(t *testing.T) {
+	v := &View{viewName: "myview"}
+	ctx := metadata.ContextWithMetadata(context.Background())
+	st := request.Request{}
+	ctx = v.Metadata(ctx, st)
+
+	if f := metadata.ValueFunc(ctx, "view/name"); f == nil {
+		t.Fatalf("metadata value func is nil")
+	} else if got := f(); got != "myview" {
+		t.Fatalf("metadata value: got %q, want %q", got, "myview")
+	}
+}