Add JSON support, more tests and comments

.gitignore

@@ -1 +1,2 @@
-.idea/
+.idea/
+dasel

README.md

@@ -1,8 +1,45 @@
 # dasel
 
-Read and modify data structures using selectors.
+[![Go Report Card](https://goreportcard.com/badge/github.com/TomWright/dasel)](https://goreportcard.com/report/github.com/TomWright/dasel)
+[![Documentation](https://godoc.org/github.com/TomWright/dasel?status.svg)](https://godoc.org/github.com/TomWright/dasel)
+![Test](https://github.com/TomWright/dasel/workflows/Test/badge.svg)
+![Build](https://github.com/TomWright/dasel/workflows/Build/badge.svg)
+
+Dasel (short for data-selector) allows you to query and modify data structures using selector strings.
+
+## Usage 
+You can import dasel as a package and use it in your applications, or you can use a pre-built binary to modify files from the command line.
+
+### Import
+As with any other go package, just use `go get`.
+```
+go get github.com/tomwright/dasel/cmd/dasel
+```
+
+### Command line
+You can `go get` the `main` package and go should automatically build and install dasel for you.
+```
+go get github.com/tomwright/dasel/cmd/dasel
+```
+
+Alternatively you can download a compiled executable from the [latest release](https://github.com/TomWright/dasel/releases/latest):
+This one liner should work for you - be sure to change the targeted release executable if needed. It currently targets `dasel_linux_amd64`.
+```
+curl -s https://api.github.com/repos/tomwright/dasel/releases/latest | grep browser_download_url | grep linux_amd64 | cut -d '"' -f 4 | wget -qi - && mv dasel_linux_amd64 dasel && chmod +x dasel
+```
+
+## Support data types
+Dasel attempts to find the correct parser for the given file type, but if that fails you can choose which parser to use with the `-p` or `--parser` flag. 
+
+- YAML - `-p yaml`
+- JSON - `-p json`
 
 ## Selectors
+
+Selectors are used to define a path through a set of data. This path is usually defined as a chain of nodes.
+
+A selector is made up of different parts separated by a dot `.`, each part being used to identify the next node in the chain.
+
 The following YAML data structure will be used as a reference in the following examples.
 ```
 name: Tom
@@ -21,26 +58,49 @@ colourCodes:
   rgb: 0000ff
 ```
 
-### Root Element
-Just use the root element name as a string.
+### Property
+Property selectors are used to reference a single property of an object.
+
+Just use the property name as a string.
+```
+$ dasel select -f ./tests/assets/example.yaml -s "name"
+Tom
+```
 - `name` == `Tom`
 
-### Child Element
-Just separate the parent element from the parent element using a `.`:
+### Child Elements
+Just separate the child element from the parent element using a `.`:
+```
+$ dasel select -f ./tests/assets/example.yaml -s "preferences.favouriteColour"
+red
+```
 - `preferences.favouriteColour` == `red`
 
 #### Index
-When you have a list, you can use square brackets to access or modify a specific item.
+When you have a list, you can use square brackets to access a specific item in the list by its index.
+```
+$ dasel select -f ./tests/assets/example.yaml -s "colours.[1]"
+green
+```
 - `colours.[0]` == `red`
 - `colours.[1]` == `green`
 - `colours.[2]` == `blue`
 
-#### Next Available Index
-Next available index selector is used when adding to a list of items.
+#### Next Available Index - WIP
+Next available index selector is used when adding to a list of items. It allows you to append to a list.
 - `colours.[]`
 
-#### Look up
-Look ups are defined in brackets and allow you to dynamically select an object to use.
+#### Dynamic
+Dynamic selectors are used with lists when you don't know the index of the item, but instead know the value of a property of an object within the list. 
+
+Look ups are defined in brackets. You can use multiple dynamic selectors within the same part to perform multiple checks.
+```
+$ dasel select -f ./tests/assets/example.yaml -s ".colourCodes.(name=red).rgb"
+ff0000
+
+$ dasel select -f ./tests/assets/example.yaml -s ".colourCodes.(name=blue)(rgb=0000ff)"
+map[name:blue rgb:0000ff]
+```
 - `.colourCodes.(name=red).rgb` == `ff0000`
 - `.colourCodes.(name=green).rgb` == `00ff00`
 - `.colourCodes.(name=blue).rgb` == `0000ff`

condition.go

@@ -2,11 +2,15 @@ package dasel
 
 import "fmt"
 
+// EqualCondition lets you check for an exact match.
 type EqualCondition struct {
-	Key   string
+	// Key is the key of the value to check against.
+	Key string
+	// Value is the value we are looking for.
 	Value string
 }
 
+// Check checks to see if other contains the required key value pair.
 func (c EqualCondition) Check(other interface{}) (bool, error) {
 	switch o := other.(type) {
 	case map[string]string:
@@ -20,6 +24,7 @@ func (c EqualCondition) Check(other interface{}) (bool, error) {
 	}
 }
 
+// Condition defines a Check we can use within dynamic selectors.
 type Condition interface {
 	Check(other interface{}) (bool, error)
 }

error.go

@@ -5,54 +5,71 @@ import (
 	"fmt"
 )
 
+// ErrMissingPreviousNode is returned when FindValue doesn't have access to the previous node.
 var ErrMissingPreviousNode = errors.New("missing previous node")
 
+// UnknownComparisonOperatorErr is returned when
 type UnknownComparisonOperatorErr struct {
 	Operator string
 }
 
+// Error returns the error message.
 func (e UnknownComparisonOperatorErr) Error() string {
 	return fmt.Sprintf("unknown comparison operator: %s", e.Operator)
 }
 
+// InvalidIndexErr is returned when a selector targets an index that does not exist.
 type InvalidIndexErr struct {
 	Index string
 }
 
+// Error returns the error message.
 func (e InvalidIndexErr) Error() string {
 	return fmt.Sprintf("invalid index: %s", e.Index)
 }
 
+// UnsupportedSelector is returned when a specific selector type is used in the wrong context.
 type UnsupportedSelector struct {
 	Selector string
 }
 
+// Error returns the error message.
 func (e UnsupportedSelector) Error() string {
 	return fmt.Sprintf("selector is not supported here: %s", e.Selector)
 }
 
+// UnsupportedTypeForSelector is returned when a selector attempts to handle a data type it can't handle.
 type UnsupportedTypeForSelector struct {
 	Selector Selector
 	Value    interface{}
 }
 
+// Error returns the error message.
 func (e UnsupportedTypeForSelector) Error() string {
 	return fmt.Sprintf("selector [%s] does not support value: %T: %v", e.Selector.Type, e.Value, e.Value)
 }
 
-type NotFound struct {
+// ValueNotFound is returned when a selector string cannot be fully resolved.
+type ValueNotFound struct {
 	Selector string
 	Node     *Node
 }
 
-func (e NotFound) Error() string {
-	return fmt.Sprintf("nothing found for selector: %s", e.Selector)
+// Error returns the error message.
+func (e ValueNotFound) Error() string {
+	var previousValue interface{}
+	if e.Node != nil && e.Node.Previous != nil {
+		previousValue = e.Node.Previous.Value
+	}
+	return fmt.Sprintf("no value found for selector: %s: %v", e.Selector, previousValue)
 }
 
+// UnexpectedPreviousNilValue is returned when the previous node contains a nil value.
 type UnexpectedPreviousNilValue struct {
 	Selector string
 }
 
+// Error returns the error message.
 func (e UnexpectedPreviousNilValue) Error() string {
 	return fmt.Sprintf("previous value is nil: %s", e.Selector)
 }

internal/command/root.go

@@ -2,18 +2,18 @@ package command
 
 import (
 	"github.com/spf13/cobra"
+	"github.com/tomwright/dasel/internal"
 )
 
+// RootCMD is the root command for use with cobra.
 var RootCMD = &cobra.Command{
-	Use:        "dasel",
-	Aliases:    nil,
-	SuggestFor: nil,
-	Short:      "A small helper to manage kubernetes configurations.",
+	Use:   "dasel",
+	Short: "Query and modify data structures using selector strings.",
 }
 
 func init() {
+	RootCMD.Version = internal.Version
 	RootCMD.AddCommand(
 		selectCommand(),
-		versionCommand(),
 	)
 }

internal/command/select.go

@@ -8,23 +8,32 @@ import (
 )
 
 func selectCommand() *cobra.Command {
-	var file, selector, parser string
+	var fileFlag, selectorFlag, parserFlag string
 
 	cmd := &cobra.Command{
 		Use:   "select -f <file> -s <selector>",
-		Short: "Select properties from the given files.",
+		Short: "Select properties from the given file.",
 		Args:  cobra.ExactArgs(0),
 		RunE: func(cmd *cobra.Command, args []string) error {
-			parser, err := storage.FromString(parser)
-			if err != nil {
-				return err
+			var parser storage.Parser
+			var err error
+			if parserFlag == "" {
+				parser, err = storage.NewParserFromFilename(fileFlag)
+				if err != nil {
+					return fmt.Errorf("could not get parser from filename: %w", err)
+				}
+			} else {
+				parser, err = storage.NewParserFromString(parserFlag)
+				if err != nil {
+					return fmt.Errorf("could not get parser: %w", err)
+				}
 			}
-			value, err := parser.LoadFromFile(file)
+			value, err := storage.LoadFromFile(fileFlag, parser)
 			if err != nil {
 				return fmt.Errorf("could not load file: %w", err)
 			}
 			rootNode := dasel.New(value)
-			res, err := rootNode.Query(selector)
+			res, err := rootNode.Query(selectorFlag)
 			if err != nil {
 				return fmt.Errorf("could not query node: %w", err)
 			}
@@ -35,9 +44,15 @@ func selectCommand() *cobra.Command {
 		},
 	}
 
-	cmd.Flags().StringVarP(&file, "file", "f", "", "The file to query.")
-	cmd.Flags().StringVarP(&selector, "selector", "s", "", "The selector to use when querying.")
-	cmd.Flags().StringVarP(&parser, "parser", "p", "yaml", "The parser to use with the given file.")
+	cmd.Flags().StringVarP(&fileFlag, "file", "f", "", "The file to query.")
+	cmd.Flags().StringVarP(&selectorFlag, "selector", "s", "", "The selector to use when querying the data structure.")
+	cmd.Flags().StringVarP(&parserFlag, "parser", "p", "", "The parser to use with the given file.")
+
+	for _, f := range []string{"file", "selector"} {
+		if err := cmd.MarkFlagRequired(f); err != nil {
+			panic("could not mark flag as required: " + f)
+		}
+	}
 
 	return cmd
 }

internal/command/version.go

@@ -1,20 +0,0 @@
-package command
-
-import (
-	"fmt"
-	"github.com/spf13/cobra"
-	"github.com/tomwright/dasel/internal"
-)
-
-func versionCommand() *cobra.Command {
-	cmd := &cobra.Command{
-		Use:   "version",
-		Short: "Prints the dasel version.",
-		Args:  cobra.ExactArgs(0),
-		Run: func(cmd *cobra.Command, args []string) {
-			fmt.Println(internal.Version)
-		},
-	}
-
-	return cmd
-}

internal/storage/json.go

@@ -0,0 +1,19 @@
+package storage
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+// JSONParser is a Parser implementation to handle yaml files.
+type JSONParser struct {
+}
+
+// FromBytes returns some Data that is represented by the given bytes.
+func (p *JSONParser) FromBytes(byteData []byte) (interface{}, error) {
+	var data interface{}
+	if err := json.Unmarshal(byteData, &data); err != nil {
+		return data, fmt.Errorf("could not unmarshal config data: %w", err)
+	}
+	return data, nil
+}

internal/storage/parser.go

@@ -2,46 +2,53 @@ package storage
 
 import (
 	"fmt"
-	"gopkg.in/yaml.v2"
 	"io/ioutil"
+	"path/filepath"
+	"strings"
 )
 
-type unknownParserErr struct {
+// UnknownParserErr is returned when an invalid parser name is given.
+type UnknownParserErr struct {
 	parser string
 }
 
-func (e unknownParserErr) Error() string {
+// Error returns the error message.
+func (e UnknownParserErr) Error() string {
 	return fmt.Sprintf("unknown parser: %s", e.parser)
 }
 
+// Parser can be used to load and save files from/to disk.
 type Parser interface {
 	FromBytes(byteData []byte) (interface{}, error)
-	LoadFromFile(filename string) (interface{}, error)
 }
 
-func FromString(parser string) (Parser, error) {
+// NewParserFromFilename returns a Parser from the given filename.
+func NewParserFromFilename(filename string) (Parser, error) {
+	ext := strings.ToLower(filepath.Ext(filename))
+	switch ext {
+	case ".yaml", ".yml":
+		return &YAMLParser{}, nil
+	case ".json":
+		return &JSONParser{}, nil
+	default:
+		return nil, &UnknownParserErr{parser: ext}
+	}
+}
+
+// NewParserFromString returns a Parser from the given parser name.
+func NewParserFromString(parser string) (Parser, error) {
 	switch parser {
 	case "yaml":
 		return &YAMLParser{}, nil
+	case "json":
+		return &JSONParser{}, nil
 	default:
-		return nil, &unknownParserErr{parser: parser}
+		return nil, &UnknownParserErr{parser: parser}
 	}
 }
 
-type YAMLParser struct {
-}
-
-// FromBytes returns some Data that is represented by the given bytes.
-func (p *YAMLParser) FromBytes(byteData []byte) (interface{}, error) {
-	var data interface{}
-	if err := yaml.Unmarshal(byteData, &data); err != nil {
-		return data, fmt.Errorf("could not unmarshal config data: %w", err)
-	}
-	return data, nil
-}
-
-// LoadFromFile loads Data from the given file.
-func (p *YAMLParser) LoadFromFile(filename string) (interface{}, error) {
+// LoadFromFile loads data from the given file.
+func LoadFromFile(filename string, p Parser) (interface{}, error) {
 	byteData, err := ioutil.ReadFile(filename)
 	if err != nil {
 		return nil, fmt.Errorf("could not read config file: %w", err)

internal/storage/yaml.go

@@ -0,0 +1,19 @@
+package storage
+
+import (
+	"fmt"
+	"gopkg.in/yaml.v2"
+)
+
+// YAMLParser is a Parser implementation to handle yaml files.
+type YAMLParser struct {
+}
+
+// FromBytes returns some Data that is represented by the given bytes.
+func (p *YAMLParser) FromBytes(byteData []byte) (interface{}, error) {
+	var data interface{}
+	if err := yaml.Unmarshal(byteData, &data); err != nil {
+		return data, fmt.Errorf("could not unmarshal config data: %w", err)
+	}
+	return data, nil
+}

node.go

@@ -39,6 +39,7 @@ type Node struct {
 	Selector Selector `json:"selector"`
 }
 
+// String returns a string representation of the node. It does this by marshaling it.
 func (n *Node) String() string {
 	b, err := json.MarshalIndent(n, "", "  ")
 	if err != nil {
@@ -113,6 +114,7 @@ func ParseSelector(selector string) (Selector, error) {
 	return sel, nil
 }
 
+// New returns a new root note with the given value.
 func New(value interface{}) *Node {
 	rootNode := &Node{
 		Previous: nil,
@@ -129,6 +131,7 @@ func New(value interface{}) *Node {
 	return rootNode
 }
 
+// Query uses the given selector to query the current node and return the result.
 func (n Node) Query(selector string) (*Node, error) {
 	n.Selector.Remaining = selector
 	rootNode := &n
@@ -159,7 +162,7 @@ func (n Node) Query(selector string) (*Node, error) {
 		nextNode.Value, err = FindValue(nextNode)
 		// Populate the value for the new node.
 		if err != nil {
-			return nil, &NotFound{Selector: nextNode.Selector.Current, Node: nextNode}
+			return nil, err
 		}
 
 		previousNode = nextNode
@@ -179,14 +182,14 @@ func findValueProperty(n *Node) (interface{}, error) {
 		if ok {
 			return v, nil
 		} else {
-			return nil, &NotFound{Selector: n.Selector.Current, Node: n}
+			return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
 		}
 	case map[interface{}]interface{}:
 		v, ok := p[n.Selector.Property]
 		if ok {
 			return v, nil
 		} else {
-			return nil, &NotFound{Selector: n.Selector.Current, Node: n}
+			return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
 		}
 	default:
 		return nil, &UnsupportedTypeForSelector{Selector: n.Selector, Value: n.Previous.Value}
@@ -204,55 +207,76 @@ func findValueIndex(n *Node) (interface{}, error) {
 		if n.Selector.Index >= 0 && n.Selector.Index < l {
 			return p[n.Selector.Index], nil
 		} else {
-			return nil, &NotFound{Selector: n.Selector.Current, Node: n}
+			return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
 		}
 	case []map[string]interface{}:
 		l := int64(len(p))
 		if n.Selector.Index >= 0 && n.Selector.Index < l {
 			return p[n.Selector.Index], nil
 		} else {
-			return nil, &NotFound{Selector: n.Selector.Current, Node: n}
+			return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
 		}
 	case map[interface{}]interface{}:
 		l := int64(len(p))
 		if n.Selector.Index >= 0 && n.Selector.Index < l {
 			return p[n.Selector.Index], nil
 		} else {
-			return nil, &NotFound{Selector: n.Selector.Current, Node: n}
+			return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
 		}
 	case map[int]interface{}:
 		l := int64(len(p))
 		if n.Selector.Index >= 0 && n.Selector.Index < l {
 			return p[int(n.Selector.Index)], nil
 		} else {
-			return nil, &NotFound{Selector: n.Selector.Current, Node: n}
+			return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
 		}
 	case []interface{}:
 		l := int64(len(p))
 		if n.Selector.Index >= 0 && n.Selector.Index < l {
 			return p[n.Selector.Index], nil
 		} else {
-			return nil, &NotFound{Selector: n.Selector.Current, Node: n}
+			return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
 		}
 	case []string:
 		l := int64(len(p))
 		if n.Selector.Index >= 0 && n.Selector.Index < l {
 			return p[n.Selector.Index], nil
 		} else {
-			return nil, &NotFound{Selector: n.Selector.Current, Node: n}
+			return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
 		}
 	case []int:
 		l := int64(len(p))
 		if n.Selector.Index >= 0 && n.Selector.Index < l {
 			return p[n.Selector.Index], nil
 		} else {
-			return nil, &NotFound{Selector: n.Selector.Current, Node: n}
+			return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
 		}
 	default:
 		return nil, &UnsupportedTypeForSelector{Selector: n.Selector, Value: n.Previous.Value}
 	}
 }
 
+// processFindDynamicItem is used by findValueDynamic.
+func processFindDynamicItem(n *Node, object interface{}) (interface{}, bool, error) {
+	// Loop through each condition.
+	allConditionsMatched := true
+	for _, c := range n.Selector.Conditions {
+		// If the object doesn't match any checks, return a ValueNotFound.
+		found, err := c.Check(object)
+		if err != nil {
+			return nil, false, err
+		}
+		if !found {
+			allConditionsMatched = false
+			break
+		}
+	}
+	if allConditionsMatched {
+		return object, true, nil
+	}
+	return nil, false, nil
+}
+
 // findValueDynamic finds the value for the given node using the dynamic selector
 // information.
 func findValueDynamic(n *Node) (interface{}, error) {
@@ -260,65 +284,49 @@ func findValueDynamic(n *Node) (interface{}, error) {
 	case nil:
 		return nil, &UnexpectedPreviousNilValue{Selector: n.Previous.Selector.Current}
 	case []map[interface{}]interface{}:
-		for _, v := range p {
-			// Loop through each condition.
-			allConditionsMatched := true
-			for _, c := range n.Selector.Conditions {
-				// If the object doesn't match any checks, return a NotFound.
-				found, err := c.Check(v)
-				if err != nil {
-					return nil, err
-				}
-				if !found {
-					allConditionsMatched = false
-					break
-				}
+		for _, object := range p {
+			value, found, err := processFindDynamicItem(n, object)
+			if err != nil {
+				return nil, err
 			}
-			if allConditionsMatched {
-				return v, nil
+			if found {
+				return value, nil
 			}
 		}
-		return nil, &NotFound{Selector: n.Selector.Current, Node: n}
+		return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
 	case []map[string]interface{}:
-		for _, v := range p {
-			// Loop through each condition.
-			allConditionsMatched := true
-			for _, c := range n.Selector.Conditions {
-				// If the object doesn't match any checks, return a NotFound.
-				found, err := c.Check(v)
-				if err != nil {
-					return nil, err
-				}
-				if !found {
-					allConditionsMatched = false
-					break
-				}
+		for _, object := range p {
+			value, found, err := processFindDynamicItem(n, object)
+			if err != nil {
+				return nil, err
 			}
-			if allConditionsMatched {
-				return v, nil
+			if found {
+				return value, nil
 			}
 		}
-		return nil, &NotFound{Selector: n.Selector.Current, Node: n}
+		return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
 	case []map[string]string:
-		for _, v := range p {
-			// Loop through each condition.
-			allConditionsMatched := true
-			for _, c := range n.Selector.Conditions {
-				// If the object doesn't match any checks, return a NotFound.
-				found, err := c.Check(v)
-				if err != nil {
-					return nil, err
-				}
-				if !found {
-					allConditionsMatched = false
-					break
-				}
+		for _, object := range p {
+			value, found, err := processFindDynamicItem(n, object)
+			if err != nil {
+				return nil, err
 			}
-			if allConditionsMatched {
-				return v, nil
+			if found {
+				return value, nil
 			}
 		}
-		return nil, &NotFound{Selector: n.Selector.Current, Node: n}
+		return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
+	case []interface{}:
+		for _, object := range p {
+			value, found, err := processFindDynamicItem(n, object)
+			if err != nil {
+				return nil, err
+			}
+			if found {
+				return value, nil
+			}
+		}
+		return nil, &ValueNotFound{Selector: n.Selector.Current, Node: n}
 	default:
 		return nil, &UnsupportedTypeForSelector{Selector: n.Selector, Value: n.Previous.Value}
 	}

node_test.go

@@ -2,7 +2,9 @@ package dasel_test
 
 import (
 	"errors"
+	"fmt"
 	"github.com/tomwright/dasel"
+	"github.com/tomwright/dasel/internal/storage"
 	"reflect"
 	"testing"
 )
@@ -114,6 +116,63 @@ func TestNode_Query(t *testing.T) {
 		}
 	})
 
+	t.Run("File", func(t *testing.T) {
+		tests := []struct {
+			Name     string
+			Selector string
+			Exp      string
+		}{
+			{Name: "Property", Selector: "name", Exp: "Tom"},
+			{Name: "ChildProperty", Selector: "preferences.favouriteColour", Exp: "red"},
+			{Name: "Index", Selector: "colours.[0]", Exp: "red"},
+			{Name: "Index", Selector: "colours.[1]", Exp: "green"},
+			{Name: "Index", Selector: "colours.[2]", Exp: "blue"},
+			{Name: "IndexProperty", Selector: "colourCodes.[0].name", Exp: "red"},
+			{Name: "IndexProperty", Selector: "colourCodes.[1].name", Exp: "green"},
+			{Name: "IndexProperty", Selector: "colourCodes.[2].name", Exp: "blue"},
+			{Name: "DynamicProperty", Selector: "colourCodes.(name=red).rgb", Exp: "ff0000"},
+			{Name: "DynamicProperty", Selector: "colourCodes.(name=green).rgb", Exp: "00ff00"},
+			{Name: "DynamicProperty", Selector: "colourCodes.(name=blue).rgb", Exp: "0000ff"},
+			{Name: "MultipleDynamicProperty", Selector: "colourCodes.(name=red)(rgb=ff0000).name", Exp: "red"},
+			{Name: "MultipleDynamicProperty", Selector: "colourCodes.(name=green)(rgb=00ff00).name", Exp: "green"},
+			{Name: "MultipleDynamicProperty", Selector: "colourCodes.(name=blue)(rgb=0000ff).name", Exp: "blue"},
+		}
+
+		fileTest := func(filename string) func(t *testing.T) {
+			return func(t *testing.T) {
+				parser, err := storage.NewParserFromFilename(filename)
+				if err != nil {
+					t.Errorf("could not get parser: %s", err)
+					return
+				}
+
+				value, err := storage.LoadFromFile(filename, parser)
+				if err != nil {
+					t.Errorf("could not load value from file: %s", err)
+					return
+				}
+
+				for _, testCase := range tests {
+					tc := testCase
+					t.Run(tc.Name, func(t *testing.T) {
+						node, err := dasel.New(value).Query(tc.Selector)
+						if err != nil {
+							t.Errorf("unexpected error: %s", err)
+							return
+						}
+
+						if exp, got := tc.Exp, fmt.Sprint(node.Value); exp != got {
+							t.Errorf("expected value `%s`, got `%s`", exp, got)
+						}
+					})
+				}
+			}
+		}
+
+		t.Run("JSON", fileTest("./tests/assets/example.json"))
+		t.Run("YAML", fileTest("./tests/assets/example.yaml"))
+	})
+
 	t.Run("Traversal", func(t *testing.T) {
 		tests := parseTest{
 			Selector: ".a.b.c.thing",

tests/assets/example.json

@@ -0,0 +1,25 @@
+{
+  "name": "Tom",
+  "preferences": {
+    "favouriteColour": "red"
+  },
+  "colours": [
+    "red",
+    "green",
+    "blue"
+  ],
+  "colourCodes": [
+    {
+      "name": "red",
+      "rgb": "ff0000"
+    },
+    {
+      "name": "green",
+      "rgb": "00ff00"
+    },
+    {
+      "name": "blue",
+      "rgb": "0000ff"
+    }
+  ]
+}