diff --git a/.github/workflows/test.yaml b/.github/workflows/test.yaml
index 81c7a10d..fd942730 100644
--- a/.github/workflows/test.yaml
+++ b/.github/workflows/test.yaml
@@ -38,7 +38,7 @@ jobs:
       - name: test
         uses: ./ci/image
         with:
-          args: go test -v -cover -covermode=count ./internal/... ./cmd/...
+          args: ./ci/steps/unit_test.sh
   gendocs:
     runs-on: ubuntu-latest
     steps:
diff --git a/ci/image/Dockerfile b/ci/image/Dockerfile
index 8eb77371..f814866d 100644
--- a/ci/image/Dockerfile
+++ b/ci/image/Dockerfile
@@ -5,3 +5,4 @@ ENV CI=true
 
 RUN go get golang.org/x/tools/cmd/goimports
 RUN go get github.com/mattn/goveralls
+RUN apt update && apt install grep
diff --git a/ci/steps/unit_test.sh b/ci/steps/unit_test.sh
new file mode 100755
index 00000000..9f7c9e13
--- /dev/null
+++ b/ci/steps/unit_test.sh
@@ -0,0 +1,9 @@
+#!/bin/bash
+
+set -euo pipefail
+
+cd "$(git rev-parse --show-toplevel)"
+
+echo "--- go test..."
+
+go test $(go list ./... | grep -v pkg/tcli | grep -v ci/integration)
diff --git a/pkg/clog/error.go b/pkg/clog/clog.go
similarity index 100%
rename from pkg/clog/error.go
rename to pkg/clog/clog.go
diff --git a/pkg/clog/clog_test.go b/pkg/clog/clog_test.go
new file mode 100644
index 00000000..8d1c88b4
--- /dev/null
+++ b/pkg/clog/clog_test.go
@@ -0,0 +1,76 @@
+package clog
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"cdr.dev/slog/sloggers/slogtest/assert"
+	"golang.org/x/xerrors"
+)
+
+func TestError(t *testing.T) {
+	t.Run("oneline", func(t *testing.T) {
+		var mockErr error = Error("fake error")
+		mockErr = xerrors.Errorf("wrap 1: %w", mockErr)
+		mockErr = fmt.Errorf("wrap 2: %w", mockErr)
+
+		reader, writer, err := os.Pipe()
+		assert.Success(t, "create pipe", err)
+
+		//! clearly not thread safe
+		os.Stderr = writer
+
+		Log(mockErr)
+		writer.Close()
+
+		output, err := ioutil.ReadAll(reader)
+		assert.Success(t, "read all stderr output", err)
+
+		assert.Equal(t, "output is as expected", "error: fake error\n\n", string(output))
+	})
+
+	t.Run("plain-error", func(t *testing.T) {
+		mockErr := xerrors.Errorf("base error")
+		mockErr = fmt.Errorf("wrap 1: %w", mockErr)
+
+		reader, writer, err := os.Pipe()
+		assert.Success(t, "create pipe", err)
+
+		//! clearly not thread safe
+		os.Stderr = writer
+
+		Log(mockErr)
+		writer.Close()
+
+		output, err := ioutil.ReadAll(reader)
+		assert.Success(t, "read all stderr output", err)
+
+		assert.Equal(t, "output is as expected", "fatal: wrap 1: base error\n\n", string(output))
+	})
+
+	t.Run("multi-line", func(t *testing.T) {
+		var mockErr error = Error("fake header", "next line", BlankLine, Tipf("content of fake tip"))
+		mockErr = xerrors.Errorf("wrap 1: %w", mockErr)
+		mockErr = fmt.Errorf("wrap 1: %w", mockErr)
+
+		reader, writer, err := os.Pipe()
+		assert.Success(t, "create pipe", err)
+
+		//! clearly not thread safe
+		os.Stderr = writer
+
+		Log(mockErr)
+		writer.Close()
+
+		output, err := ioutil.ReadAll(reader)
+		assert.Success(t, "read all stderr output", err)
+
+		assert.Equal(t,
+			"output is as expected",
+			"error: fake header\n  | next line\n  | \n  | tip: content of fake tip\n\n",
+			string(output),
+		)
+	})
+}