feat(do): add new Do function to simplify golden usage

Add new Do function whihc ecapsulates the common pattern of writing to
golden file if the update mechnism evaluates to true, followed by
immediately reading the file. Compresses four lines into one.

Author: jimeh

Makefile

@@ -33,6 +33,7 @@ SHELL := env \
 #
 # Tools
 #
+
 # external tool
 define tool # 1: binary-name, 2: go-import-path
 TOOLS += $(TOOLDIR)/$(1)

README.md

@@ -28,22 +28,28 @@ import "github.com/jimeh/go-golden"
 
 ```go
 func TestExampleMyStruct(t *testing.T) {
-	got, err := json.Marshal(&MyStruct{Foo: "Bar"})
-	require.NoError(t, err)
+    got, err := json.Marshal(&MyStruct{Foo: "Bar"})
+    require.NoError(t, err)
 
-	if golden.Update() {
-		golden.Set(t, got)
-	}
-	want := golden.Get(t)
+    want := golden.Do(t, got)
 
-	assert.Equal(t, want, got)
+    assert.Equal(t, want, got)
 }
 ```
 
 The above example will read/write to:
 
 - `testdata/TestExampleMyStruct.golden`
 
+The call to `golden.Do()` is equivalent to:
+
+```go
+if golden.Update() {
+    golden.Set(t, got)
+}
+want := golden.Get(t)
+```
+
 To update the golden file (have `golden.Update()` return `true`), simply set the
 `GOLDEN_UPDATE` environment variable to one of `1`, `y`, `t`, `yes`, `on`, or
 `true` when running tests.

example_test.go

@@ -10,6 +10,9 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+// The tests in this file are examples from the README and the package-level Go
+// documentation.
+
 type MyStruct struct {
 	Foo string `json:"foo,omitempty"`
 }
@@ -21,10 +24,7 @@ func TestExampleMyStruct(t *testing.T) {
 	got, err := json.Marshal(&MyStruct{Foo: "Bar"})
 	require.NoError(t, err)
 
-	if golden.Update() {
-		golden.Set(t, got)
-	}
-	want := golden.Get(t)
+	want := golden.Do(t, got)
 
 	assert.Equal(t, want, got)
 }
@@ -46,10 +46,7 @@ func TestExampleMyStructTabular(t *testing.T) {
 			got, err := json.Marshal(tt.obj)
 			require.NoError(t, err)
 
-			if golden.Update() {
-				golden.Set(t, got)
-			}
-			want := golden.Get(t)
+			want := golden.Do(t, got)
 
 			assert.Equal(t, want, got)
 		})
@@ -64,13 +61,11 @@ func TestExampleMyStructP(t *testing.T) {
 	gotJSON, _ := json.Marshal(&MyStruct{Foo: "Bar"})
 	gotXML, _ := xml.Marshal(&MyStruct{Foo: "Bar"})
 
-	if golden.Update() {
-		golden.SetP(t, "json", gotJSON)
-		golden.SetP(t, "xml", gotXML)
-	}
+	wantJSON := golden.DoP(t, "json", gotJSON)
+	wantXML := golden.DoP(t, "xml", gotXML)
 
-	assert.Equal(t, golden.GetP(t, "json"), gotJSON)
-	assert.Equal(t, golden.GetP(t, "xml"), gotXML)
+	assert.Equal(t, wantJSON, gotJSON)
+	assert.Equal(t, wantXML, gotXML)
 }
 
 // TestExampleMyStructTabularP reads/writes the following golden file:
@@ -92,13 +87,11 @@ func TestExampleMyStructTabularP(t *testing.T) {
 			gotJSON, _ := json.Marshal(tt.obj)
 			gotXML, _ := xml.Marshal(tt.obj)
 
-			if golden.Update() {
-				golden.SetP(t, "json", gotJSON)
-				golden.SetP(t, "xml", gotXML)
-			}
+			wantJSON := golden.DoP(t, "json", gotJSON)
+			wantXML := golden.DoP(t, "xml", gotXML)
 
-			assert.Equal(t, golden.GetP(t, "json"), gotJSON)
-			assert.Equal(t, golden.GetP(t, "xml"), gotXML)
+			assert.Equal(t, wantJSON, gotJSON)
+			assert.Equal(t, wantXML, gotXML)
 		})
 	}
 }