Add error message string matchers

Author: feketegy

matchers.go

@@ -0,0 +1,34 @@
+package errors
+
+import "strings"
+
+// HasMessage reports whether any error in err's chain matches msg. It performs a case-insensitive matching.
+//
+// This is helpful when the error type's in err's chain is unknown and a string matching is preferred.
+func HasMessage(err error, msg string) bool {
+	errs := Flatten(err)
+
+	for _, e := range errs {
+		if strings.EqualFold(e.Msg, msg) {
+			return true
+		}
+	}
+
+	return false
+}
+
+// ContainsMessage reports whether any error in err's chain contains msg. It performs a case-insensitive matching.
+//
+// This is helpful when the error type's in err's chain is unknown and a string matching is preferred.
+func ContainsMessage(err error, msg string) bool {
+	errs := Flatten(err)
+	lowerMsg := strings.ToLower(msg)
+
+	for _, e := range errs {
+		if strings.Contains(strings.ToLower(e.Msg), lowerMsg) {
+			return true
+		}
+	}
+
+	return false
+}

matchers_test.go

@@ -0,0 +1,65 @@
+package errors
+
+import (
+	"testing"
+)
+
+func TestMatchers(t *testing.T) {
+	t.Run("it should match message", itShouldMatchMessage)
+	t.Run("it should match containing message", itShouldMatchContainingMessage)
+}
+
+func itShouldMatchMessage(t *testing.T) {
+	err1 := E("this is an error", WithMeta("key1", "val1"))
+	err2 := E("this is error2", err1, WithMeta("key2", "val2"))
+
+	has := HasMessage(err2, "this is an error")
+	if has == false {
+		t.Fatalf("HasMessage() return expected true, got false")
+	}
+
+	has = HasMessage(err1, "this is an error")
+	if has == false {
+		t.Fatalf("HasMessage() should match a single err chain")
+	}
+
+	has = HasMessage(err2, "this is error2")
+	if has == false {
+		t.Fatalf("HasMessage() should match the top-most wrapped error in the chain")
+	}
+
+	has = HasMessage(err2, "ThIs Is An ErRor")
+	if has == false {
+		t.Fatalf("HasMessage() match should be case-insensitive")
+	}
+
+	has = HasMessage(err2, "error2")
+	if has == true {
+		t.Fatalf("HasMessage() should match exact messages")
+	}
+}
+
+func itShouldMatchContainingMessage(t *testing.T) {
+	err1 := E("this is an error", WithMeta("key1", "val1"))
+	err2 := E("this is error2", err1, WithMeta("key2", "val2"))
+
+	has := ContainsMessage(err2, "an error")
+	if has == false {
+		t.Fatalf("ContainsMessage() should match partial messages")
+	}
+
+	has = ContainsMessage(err2, "an erROR")
+	if has == false {
+		t.Fatalf("ContainsMessage() should match case-insensitive partial messages")
+	}
+
+	has = ContainsMessage(err1, "an erROR")
+	if has == false {
+		t.Fatalf("ContainsMessage() should match a single err chain")
+	}
+
+	has = ContainsMessage(err2, "erROR2")
+	if has == false {
+		t.Fatalf("ContainsMessage() should match the top-most wrapped error in the chain")
+	}
+}