Add tests for errors

rpc/messages_test.go

+package rpc
+
+import (
+	"testing"
+)
+
+func TestInsufficientParamsError(t *testing.T) {
+	err := NewInsufficientParamsError(0, 1)
+	expected := "insufficient params, want 1 have 0"
+
+	if err.Error() != expected {
+		t.Error(err.Error())
+	}
+}
+
+func TestNotImplementedError(t *testing.T) {
+	err := NewNotImplementedError("foo")
+	expected := "foo method not implemented"
+
+	if err.Error() != expected {
+		t.Error(err.Error())
+	}
+}
+
+func TestDecodeParamError(t *testing.T) {
+	err := NewDecodeParamError("foo")
+	expected := "could not decode, foo"
+
+	if err.Error() != expected {
+		t.Error(err.Error())
+	}
+}
+
+func TestValidationError(t *testing.T) {
+	err := NewValidationError("foo", "should be `bar`")
+	expected := "foo not valid, should be `bar`"
+
+	if err.Error() != expected {
+		t.Error(err.Error())
+	}
+}