Refine custom matcher

helper.go

@@ -219,6 +219,9 @@ func formatValueInline(v interface{}) string {
 		string:
 		return formatValue(v)
 
+	case *CallbackMatch:
+		return formatValue(m.matcher())
+
 	case Matcher:
 		return fmt.Sprintf("%T(%q)", v, m.Expected())
 
@@ -232,12 +235,15 @@ func formatType(v interface{}) string {
 		return ""
 	}
 
-	switch v.(type) {
+	switch m := v.(type) {
 	case *ExactMatch,
 		[]byte,
 		string:
 		return ""
 
+	case *CallbackMatch:
+		return formatType(m.matcher())
+
 	default:
 		return fmt.Sprintf(" using %T", v)
 	}
@@ -249,6 +255,9 @@ func formatValue(v interface{}) string {
 	}
 
 	switch m := v.(type) {
+	case *CallbackMatch:
+		return formatValue(m.matcher())
+
 	case Matcher:
 		return m.Expected()
 

helper_test.go

@@ -106,6 +106,13 @@ func TestFormatValueInline(t *testing.T) {
 			value:    "expected",
 			expected: "expected",
 		},
+		{
+			scenario: "Callback",
+			value: Match(func() Matcher {
+				return Exact("expected")
+			}),
+			expected: "expected",
+		},
 		{
 			scenario: "Matcher",
 			value:    JSON("{}"),
@@ -158,6 +165,13 @@ func TestFormatType(t *testing.T) {
 			value:    "expected",
 			expected: "",
 		},
+		{
+			scenario: "Callback",
+			value: Match(func() Matcher {
+				return Exact("expected")
+			}),
+			expected: "",
+		},
 		{
 			scenario: "Matcher",
 			value:    JSON("{}"),
@@ -197,6 +211,13 @@ func TestFormatValue(t *testing.T) {
 			value:    "expected",
 			expected: "expected",
 		},
+		{
+			scenario: "Callback",
+			value: Match(func() Matcher {
+				return Exact("expected")
+			}),
+			expected: "expected",
+		},
 		{
 			scenario: "ExactMatch",
 			value:    Exact("expected"),

matcher.go

@@ -62,25 +62,32 @@ func (m *RegexMatch) Match(actual string) bool {
 
 // CallbackMatch matches by calling a function.
 type CallbackMatch struct {
-	expect func() string
-	match  func(actual string) bool
+	callback func() Matcher
+	upstream Matcher
+}
+
+func (m *CallbackMatch) matcher() Matcher {
+	if m.upstream == nil {
+		m.upstream = m.callback()
+	}
+
+	return m.upstream
 }
 
 // Expected returns the expectation.
 func (m *CallbackMatch) Expected() string {
-	return m.expect()
+	return m.matcher().Expected()
 }
 
 // Match determines if the actual is expected.
 func (m *CallbackMatch) Match(actual string) bool {
-	return m.match(actual)
+	return m.matcher().Match(actual)
 }
 
 // Match creates a callback matcher.
-func Match(expect func() string, match func(actual string) bool) Matcher {
+func Match(callback func() Matcher) Matcher {
 	return &CallbackMatch{
-		expect: expect,
-		match:  match,
+		callback: callback,
 	}
 }
 
@@ -110,6 +117,9 @@ func ValueMatcher(v interface{}) Matcher {
 	case Matcher:
 		return val
 
+	case func() Matcher:
+		return Match(val)
+
 	case []byte:
 		return Exact(string(val))
 

matcher_test.go

@@ -170,22 +170,6 @@ func TestRegexMatch_Match(t *testing.T) {
 	}
 }
 
-func TestCallbackMatch(t *testing.T) {
-	t.Parallel()
-
-	m := Match(
-		func() string {
-			return "expected"
-		},
-		func(string) bool {
-			return false
-		},
-	)
-
-	assert.Equal(t, "expected", m.Expected())
-	assert.False(t, m.Match("actual"))
-}
-
 func TestValueMatcher(t *testing.T) {
 	t.Parallel()
 
@@ -231,6 +215,18 @@ func TestValueMatcher(t *testing.T) {
 	}
 }
 
+func TestValueMatcher_Match(t *testing.T) {
+	t.Parallel()
+
+	m := ValueMatcher(func() Matcher {
+		return Exact("expected")
+	})
+
+	assert.Equal(t, "expected", m.Expected())
+	assert.True(t, m.Match("expected"))
+	assert.False(t, m.Match("Mismatch"))
+}
+
 func TestValueMatcher_Panic(t *testing.T) {
 	t.Parallel()