test: add unit tests

test/teotipi_test.gleam

@@ -0,0 +1,65 @@
+import gleam/string
+import gleeunit
+import gleeunit/should
+import teotipi
+
+pub fn main() -> Nil {
+  gleeunit.main()
+}
+
+pub fn totp_string_test() {
+  "GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ"
+  |> teotipi.totp_string
+  |> should.be_ok
+  |> string.length
+  |> should.equal(6)
+}
+
+pub fn totp_string_padding_test() {
+  "GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ"
+  |> teotipi.totp_string
+  |> should.be_ok
+}
+
+pub fn totp_string_invalid_secret_test() {
+  teotipi.totp_string("INVALID!!!")
+  |> should.be_error
+}
+
+pub fn totp_function_test() {
+  let code =
+    "GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ"
+    |> teotipi.totp
+    |> should.be_ok
+
+  should.be_true(code > 0)
+  should.be_true(code < 1_000_000)
+}
+
+pub fn totp_invalid_secret_test() {
+  teotipi.totp("INVALID!!!")
+  |> should.be_error
+}
+
+pub fn totp_consistency_test() {
+  let secret = "GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ"
+  let result1 = teotipi.totp(secret)
+  let result2 = teotipi.totp(secret)
+
+  should.equal(result1, result2)
+}
+
+pub fn totp_different_secrets_test() {
+  let code1 =
+    "GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ"
+    |> teotipi.totp
+    |> should.be_ok
+
+  let code2 =
+    "JBSWY3DPEHPK3PXPJBSWY3DPEHPK3PXP"
+    |> teotipi.totp
+    |> should.be_ok
+
+  should.be_true(code1 > 0)
+  should.be_true(code2 > 0)
+}