Fixes #229 - show diffs for structs/maps/arrays/slices when Equal fails

assert/assertions.go

@@ -13,6 +13,9 @@ import (
 	"time"
 	"unicode"
 	"unicode/utf8"
+
+	"github.com/davecgh/go-spew/spew"
+	"github.com/pmezard/go-difflib/difflib"
 )
 
 // TestingT is an interface wrapper around *testing.T
@@ -233,8 +236,9 @@ func IsType(t TestingT, expectedType interface{}, object interface{}, msgAndArgs
 func Equal(t TestingT, expected, actual interface{}, msgAndArgs ...interface{}) bool {
 
 	if !ObjectsAreEqual(expected, actual) {
+		diff := diff(expected, actual)
 		return Fail(t, fmt.Sprintf("Not equal: %#v (expected)\n"+
-			"        != %#v (actual)", expected, actual), msgAndArgs...)
+			"        != %#v (actual)%s", expected, actual, diff), msgAndArgs...)
 	}
 
 	return true
@@ -921,3 +925,48 @@ func JSONEq(t TestingT, expected string, actual string, msgAndArgs ...interface{
 
 	return Equal(t, expectedJSONAsInterface, actualJSONAsInterface, msgAndArgs...)
 }
+
+func typeAndKind(v interface{}) (reflect.Type, reflect.Kind) {
+	t := reflect.TypeOf(v)
+	k := t.Kind()
+
+	if k == reflect.Ptr {
+		t = t.Elem()
+		k = t.Kind()
+	}
+	return t, k
+}
+
+// diff returns a diff of both values as long as both are of the same type and
+// are a struct, map, slice or array. Otherwise it returns an empty string.
+func diff(expected interface{}, actual interface{}) string {
+	if expected == nil || actual == nil {
+		return ""
+	}
+
+	et, ek := typeAndKind(expected)
+	at, _ := typeAndKind(actual)
+
+	if et != at {
+		return ""
+	}
+
+	if ek != reflect.Struct && ek != reflect.Map && ek != reflect.Slice && ek != reflect.Array {
+		return ""
+	}
+
+	e := spew.Sdump(expected)
+	a := spew.Sdump(actual)
+
+	diff, _ := difflib.GetUnifiedDiffString(difflib.UnifiedDiff{
+		A:        difflib.SplitLines(e),
+		B:        difflib.SplitLines(a),
+		FromFile: "Expected",
+		FromDate: "",
+		ToFile:   "Actual",
+		ToDate:   "",
+		Context:  1,
+	})
+
+	return "\n\nDiff:\n" + diff
+}

assert/assertions_test.go

@@ -984,3 +984,77 @@ func TestJSONEq_ArraysOfDifferentOrder(t *testing.T) {
 	mockT := new(testing.T)
 	False(t, JSONEq(mockT, `["foo", {"hello": "world", "nested": "hash"}]`, `[{ "hello": "world", "nested": "hash"}, "foo"]`))
 }
+
+func TestDiff(t *testing.T) {
+	expected := `
+
+Diff:
+--- Expected
++++ Actual
+@@ -1,3 +1,3 @@
+ (struct { foo string }) {
+- foo: (string) (len=5) "hello"
++ foo: (string) (len=3) "bar"
+ }
+`
+	actual := diff(
+		struct{ foo string }{"hello"},
+		struct{ foo string }{"bar"},
+	)
+	Equal(t, expected, actual)
+
+	expected = `
+
+Diff:
+--- Expected
++++ Actual
+@@ -2,5 +2,5 @@
+  (int) 1,
+- (int) 2,
+  (int) 3,
+- (int) 4
++ (int) 5,
++ (int) 7
+ }
+`
+	actual = diff(
+		[]int{1, 2, 3, 4},
+		[]int{1, 3, 5, 7},
+	)
+	Equal(t, expected, actual)
+
+	expected = `
+
+Diff:
+--- Expected
++++ Actual
+@@ -2,4 +2,4 @@
+  (int) 1,
+- (int) 2,
+- (int) 3
++ (int) 3,
++ (int) 5
+ }
+`
+	actual = diff(
+		[]int{1, 2, 3, 4}[0:3],
+		[]int{1, 3, 5, 7}[0:3],
+	)
+	Equal(t, expected, actual)
+
+	// output for maps cannot be equally tested since order is random
+	actual = diff(
+		map[string]int{"one": 1, "two": 2, "three": 3, "four": 4},
+		map[string]int{"one": 1, "three": 3, "five": 5, "seven": 7},
+	)
+	NotZero(t, len(actual))
+}
+
+func TestDiffEmptyCases(t *testing.T) {
+	Equal(t, "", diff(nil, nil))
+	Equal(t, "", diff(struct{ foo string }{}, nil))
+	Equal(t, "", diff(nil, struct{ foo string }{}))
+	Equal(t, "", diff(1, 2))
+	Equal(t, "", diff(1, 2))
+	Equal(t, "", diff([]int{1}, []bool{true}))
+}