diff --git a/caddyconfig/configadapters_test.go b/caddyconfig/configadapters_test.go
new file mode 100644
index 000000000..380a68c06
--- /dev/null
+++ b/caddyconfig/configadapters_test.go
@@ -0,0 +1,221 @@
+package caddyconfig
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestJSON(t *testing.T) {
+	tests := []struct {
+		name         string
+		val          any
+		wantNil      bool
+		wantWarnings int
+		nilWarnings  bool // pass nil warnings pointer
+	}{
+		{
+			name:         "simple string",
+			val:          "hello",
+			wantNil:      false,
+			wantWarnings: 0,
+		},
+		{
+			name:         "struct",
+			val:          struct{ Name string }{"test"},
+			wantNil:      false,
+			wantWarnings: 0,
+		},
+		{
+			name:         "nil value",
+			val:          nil,
+			wantNil:      false, // json.Marshal(nil) returns "null"
+			wantWarnings: 0,
+		},
+		{
+			name:         "map",
+			val:          map[string]string{"key": "val"},
+			wantNil:      false,
+			wantWarnings: 0,
+		},
+		{
+			name:         "unmarshalable value produces warning",
+			val:          make(chan int),
+			wantNil:      true,
+			wantWarnings: 1,
+		},
+		{
+			name:        "unmarshalable value with nil warnings pointer",
+			val:         make(chan int),
+			wantNil:     true,
+			nilWarnings: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var warnings *[]Warning
+			if !tt.nilWarnings {
+				w := []Warning{}
+				warnings = &w
+			}
+
+			result := JSON(tt.val, warnings)
+
+			if tt.wantNil && result != nil {
+				t.Errorf("JSON() = %v, want nil", string(result))
+			}
+			if !tt.wantNil && result == nil {
+				t.Error("JSON() = nil, want non-nil")
+			}
+			if warnings != nil && len(*warnings) != tt.wantWarnings {
+				t.Errorf("JSON() produced %d warnings, want %d", len(*warnings), tt.wantWarnings)
+			}
+		})
+	}
+}
+
+func TestJSONModuleObject(t *testing.T) {
+	tests := []struct {
+		name         string
+		val          any
+		fieldName    string
+		fieldVal     string
+		wantNil      bool
+		wantField    bool
+		wantWarnings int
+	}{
+		{
+			name:         "simple struct",
+			val:          struct{ Name string }{"test"},
+			fieldName:    "handler",
+			fieldVal:     "file_server",
+			wantNil:      false,
+			wantField:    true,
+			wantWarnings: 0,
+		},
+		{
+			name:         "map value",
+			val:          map[string]any{"key": "val"},
+			fieldName:    "module",
+			fieldVal:     "my_module",
+			wantNil:      false,
+			wantField:    true,
+			wantWarnings: 0,
+		},
+		{
+			name:         "non-object type (string) produces warning",
+			val:          "not-an-object",
+			fieldName:    "handler",
+			fieldVal:     "test",
+			wantNil:      true,
+			wantField:    false,
+			wantWarnings: 1,
+		},
+		{
+			name:         "unmarshalable value produces warning",
+			val:          make(chan int),
+			fieldName:    "handler",
+			fieldVal:     "test",
+			wantNil:      true,
+			wantField:    false,
+			wantWarnings: 1,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			warnings := []Warning{}
+			result := JSONModuleObject(tt.val, tt.fieldName, tt.fieldVal, &warnings)
+
+			if tt.wantNil && result != nil {
+				t.Errorf("JSONModuleObject() = %v, want nil", string(result))
+			}
+			if !tt.wantNil && result == nil {
+				t.Error("JSONModuleObject() = nil, want non-nil")
+			}
+			if len(warnings) != tt.wantWarnings {
+				t.Errorf("JSONModuleObject() produced %d warnings, want %d", len(warnings), tt.wantWarnings)
+			}
+			if tt.wantField && result != nil {
+				var m map[string]any
+				if err := json.Unmarshal(result, &m); err != nil {
+					t.Fatalf("failed to unmarshal result: %v", err)
+				}
+				if v, ok := m[tt.fieldName]; !ok {
+					t.Errorf("expected field %q in result", tt.fieldName)
+				} else if v != tt.fieldVal {
+					t.Errorf("field %q = %v, want %v", tt.fieldName, v, tt.fieldVal)
+				}
+			}
+		})
+	}
+}
+
+func TestJSONModuleObjectPreservesExistingFields(t *testing.T) {
+	val := struct {
+		Name string `json:"name"`
+		Port int    `json:"port"`
+	}{"example", 8080}
+
+	warnings := []Warning{}
+	result := JSONModuleObject(val, "handler", "static", &warnings)
+
+	if result == nil {
+		t.Fatal("expected non-nil result")
+	}
+
+	var m map[string]any
+	if err := json.Unmarshal(result, &m); err != nil {
+		t.Fatalf("failed to unmarshal: %v", err)
+	}
+
+	if m["name"] != "example" {
+		t.Errorf("name = %v, want 'example'", m["name"])
+	}
+	if m["port"] != float64(8080) {
+		t.Errorf("port = %v, want 8080", m["port"])
+	}
+	if m["handler"] != "static" {
+		t.Errorf("handler = %v, want 'static'", m["handler"])
+	}
+}
+
+func TestGetAdapterNil(t *testing.T) {
+	adapter := GetAdapter("nonexistent_adapter_xyz")
+	if adapter != nil {
+		t.Error("expected nil for unregistered adapter")
+	}
+}
+
+func TestWarningString(t *testing.T) {
+	tests := []struct {
+		name    string
+		warning Warning
+		want    string
+	}{
+		{
+			name:    "all fields",
+			warning: Warning{File: "Caddyfile", Line: 10, Directive: "reverse_proxy", Message: "upstream not found"},
+			want:    "Caddyfile:10 (reverse_proxy): upstream not found",
+		},
+		{
+			name:    "no directive",
+			warning: Warning{File: "Caddyfile", Line: 5, Message: "something off"},
+			want:    "Caddyfile:5: something off",
+		},
+		{
+			name:    "zero line",
+			warning: Warning{File: "config.json", Line: 0, Message: "invalid"},
+			want:    "config.json:0: invalid",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := tt.warning.String()
+			if got != tt.want {
+				t.Errorf("Warning.String() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}