diff --git a/cmd/mstdn/main_test.go b/cmd/mstdn/main_test.go
new file mode 100644
index 0000000..4dce09f
--- /dev/null
+++ b/cmd/mstdn/main_test.go
@@ -0,0 +1,55 @@
+package main
+
+import (
+	"os"
+	"testing"
+)
+
+func TestReadFileFile(t *testing.T) {
+	b, err := readFile("main.go")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(b) == 0 {
+		t.Fatalf("should read something: %v", err)
+	}
+}
+
+func TestReadFileStdin(t *testing.T) {
+	f, err := os.Open("main.go")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	stdin := os.Stdin
+	os.Stdin = f
+	defer func() {
+		os.Stdin = stdin
+	}()
+
+	b, err := readFile("-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(b) == 0 {
+		t.Fatalf("should read something: %v", err)
+	}
+}
+
+func TestTextContent(t *testing.T) {
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{input: "", want: ""},
+		{input: "<p>foo</p>", want: "foo"},
+		{input: "<p>foo<span>\nbar\n</span>baz</p>", want: "foobarbaz"},
+		{input: "<p>foo<span>\nbar<br></span>baz</p>", want: "foobar\nbaz"},
+	}
+	for _, test := range tests {
+		got := textContent(test.input)
+		if got != test.want {
+			t.Fatalf("want %q but %q", test.want, got)
+		}
+	}
+}