Add custom ShouldUpdate function (+minor configuration refactor) (#23)

config.go

@@ -3,14 +3,27 @@ package cupaloy
 // Configurator is a functional option that can be passed to cupaloy.New() to change snapshotting behaviour.
 type Configurator func(*config)
 
-// EnvVariableName can be used to customize the environment variable that determines whether snapshots should be updated.
+// EnvVariableName can be used to customize the environment variable that determines whether snapshots should be updated
 // e.g.
 //  cupaloy.New(EnvVariableName("UPDATE"))
 // Will create an instance where snapshots will be updated if the UPDATE environment variable is set,
 // instead of the default of UPDATE_SNAPSHOTS.
 func EnvVariableName(name string) Configurator {
 	return func(c *config) {
-		c.envVariable = name
+		c.shouldUpdate = func() bool {
+			return envVariableSet(name)
+		}
+	}
+}
+
+// ShouldUpdate can be used to provide custom logic to decide whether or not to update a snapshot
+// e.g.
+//   var update = flag.Bool("update", false, "update snapshots")
+//   cupaloy.New(ShouldUpdate(func () bool { return *update })
+// Will create an instance where snapshots are updated if the --update flag is passed to go test.
+func ShouldUpdate(f func() bool) Configurator {
+	return func(c *config) {
+		c.shouldUpdate = f
 	}
 }
 
@@ -25,19 +38,13 @@ func SnapshotSubdirectory(name string) Configurator {
 }
 
 type config struct {
-	envVariable       string
-	subDirName        string
-	snapshotExtension string
+	shouldUpdate func() bool
+	subDirName   string
 }
 
 func defaultConfig() *config {
-	return &config{
-		envVariable:       "UPDATE_SNAPSHOTS",
-		subDirName:        ".snapshots",
-		snapshotExtension: "",
-	}
-}
-
-func (c *config) shouldUpdate() bool {
-	return envVariableSet(c.envVariable)
+	c := &config{}
+	SnapshotSubdirectory(".snapshots")(c)
+	EnvVariableName("UPDATE_SNAPSHOTS")(c)
+	return c
 }

examples/.snapshots/examples_test-TestShouldUpdate-func1

@@ -0,0 +1 @@
+(string) (len=5) "Hello"

examples/.snapshots/examples_test-TestShouldUpdate-func2

@@ -0,0 +1 @@
+(string) (len=5) "Hello"

examples/advanced_test.go

@@ -2,6 +2,7 @@ package examples_test
 
 import (
 	"io/ioutil"
+	"strings"
 	"testing"
 
 	"github.com/bradleyjkemp/cupaloy"
@@ -84,3 +85,28 @@ func TestMultipleSnapshots(t *testing.T) {
 		cupaloy.New().SnapshotT(t, result2)
 	})
 }
+
+// Test the ShouldUpdate configurator
+func TestShouldUpdate(t *testing.T) {
+	t.Run("false", func(t *testing.T) {
+		result := "Hello!"
+		err := cupaloy.New(cupaloy.ShouldUpdate(func() bool { return false })).Snapshot(result)
+		if err == nil || !strings.Contains(err.Error(), "not equal") {
+			// not updating snapshot so error should contain a diff
+			t.Fatal(err)
+		}
+	})
+
+	t.Run("true", func(t *testing.T) {
+		result := "Hello!"
+		c := cupaloy.New(cupaloy.ShouldUpdate(func() bool { return true }))
+		err := c.Snapshot(result)
+		if err == nil || !strings.Contains(err.Error(), "updated") {
+			// snapshot should have been updated with error signalling this
+			t.Fatal(err)
+		}
+
+		// snapshot again with old value to revert the update
+		c.Snapshot("Hello")
+	})
+}

util.go

@@ -35,7 +35,7 @@ func envVariableSet(envVariable string) bool {
 }
 
 func (c *config) snapshotFilePath(testName string) string {
-	return filepath.Join(c.subDirName, testName+c.snapshotExtension)
+	return filepath.Join(c.subDirName, testName)
 }
 
 func takeSnapshot(i ...interface{}) string {