diff --git a/apps/app-runner/log_test.go b/apps/app-runner/log_test.go
new file mode 100644
index 0000000..777cf8f
--- /dev/null
+++ b/apps/app-runner/log_test.go
@@ -0,0 +1,38 @@
+package main
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestLoggerWriteFullLine(t *testing.T) {
+	l := NewLogger("foo")
+	fmt.Fprintf(l, "hi\n")
+	c, err := l.Contents()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if c != "hi\n" {
+		t.Fatal(c)
+	}
+}
+
+func TestLoggerWritePartialLine(t *testing.T) {
+	l := NewLogger("foo")
+	fmt.Fprintf(l, "hi\nfoo")
+	c, err := l.Contents()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if c != "hi\n" {
+		t.Fatal(c)
+	}
+	fmt.Fprintf(l, "bar\n")
+	c, err = l.Contents()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if c != "hi\nfoobar\n" {
+		t.Fatal(c)
+	}
+}