From 56b93642b10c13d8c6ddc846143831316b2dce85 Mon Sep 17 00:00:00 2001
From: Lukas Obermann <lukas.obermann@icloud.com>
Date: Tue, 31 Oct 2023 14:41:00 +0100
Subject: [PATCH] test: add tests for maybe and type safety modules

---
 src/shared/utils/maybe.test.ts      | 102 ++++++++++++++++++++++++++++
 src/shared/utils/typeSafety.test.ts |  13 ++++
 2 files changed, 115 insertions(+)
 create mode 100644 src/shared/utils/maybe.test.ts
 create mode 100644 src/shared/utils/typeSafety.test.ts

diff --git a/src/shared/utils/maybe.test.ts b/src/shared/utils/maybe.test.ts
new file mode 100644
index 00000000..a0286446
--- /dev/null
+++ b/src/shared/utils/maybe.test.ts
@@ -0,0 +1,102 @@
+import assert from "node:assert/strict"
+import { describe, it } from "node:test"
+import { Just, Nothing, combine, fromNullable, isJust, isNothing, map, reduce } from "./maybe.ts"
+
+describe(Just.name, () => {
+  it("creates a maybe that contains a value", () => {
+    const maybe = Just("hello")
+    assert.deepEqual(maybe, { tag: "Just", value: "hello" })
+  })
+})
+
+describe("Nothing", () => {
+  it("creates a maybe that contains nothing", () => {
+    const maybe = Nothing
+    assert.deepEqual(maybe, { tag: "Nothing" })
+  })
+})
+
+describe(isJust.name, () => {
+  it("returns true if the maybe contains a value", () => {
+    const maybe = Just("hello")
+    assert.equal(isJust(maybe), true)
+  })
+
+  it("returns false if the maybe contains nothing", () => {
+    const maybe = Nothing
+    assert.equal(isJust(maybe), false)
+  })
+})
+
+describe(isNothing.name, () => {
+  it("returns true if the maybe contains nothing", () => {
+    const maybe = Nothing
+    assert.equal(isNothing(maybe), true)
+  })
+
+  it("returns false if the maybe contains a value", () => {
+    const maybe = Just("hello")
+    assert.equal(isNothing(maybe), false)
+  })
+})
+
+describe(fromNullable.name, () => {
+  it("creates a maybe that contains a value if the input is not null or undefined", () => {
+    const maybe = fromNullable("hello")
+    assert.deepEqual(maybe, { tag: "Just", value: "hello" })
+  })
+
+  it("creates a maybe that contains nothing if the input is null", () => {
+    const maybe = fromNullable(null)
+    assert.deepEqual(maybe, { tag: "Nothing" })
+  })
+
+  it("creates a maybe that contains nothing if the input is undefined", () => {
+    const maybe = fromNullable(undefined)
+    assert.deepEqual(maybe, { tag: "Nothing" })
+  })
+})
+
+describe(reduce.name, () => {
+  it("returns the default value if the maybe contains nothing", () => {
+    const maybe = Nothing
+    const result = reduce<string, string>(maybe, "default", value => value.toUpperCase())
+    assert.equal(result, "default")
+  })
+
+  it("applies the function to the value if the maybe contains a value", () => {
+    const maybe = Just("hello")
+    const result = reduce(maybe, "default", value => value.toUpperCase())
+    assert.equal(result, "HELLO")
+  })
+})
+
+describe(map.name, () => {
+  it("returns a maybe that contains nothing if the input maybe contains nothing", () => {
+    const maybe = Nothing
+    const result = map<string, string>(maybe, value => value.toUpperCase())
+    assert.deepEqual(result, { tag: "Nothing" })
+  })
+
+  it("applies the function to the value if the input maybe contains a value", () => {
+    const maybe = Just("hello")
+    const result = map(maybe, value => value.toUpperCase())
+    assert.deepEqual(result, { tag: "Just", value: "HELLO" })
+  })
+})
+
+describe(combine.name, () => {
+  it("returns a maybe that contains nothing if either input maybe contains nothing", () => {
+    const maybe1 = Just("hello")
+    const maybe2 = Nothing
+    const result = combine(maybe1, maybe2, (value1, value2) => value1 + value2)
+    assert.deepEqual(result, { tag: "Nothing" })
+  })
+
+  it("applies the function to the values if both input maybes contain a value", () => {
+    const maybe1 = Just("hello")
+    const maybe2 = Just("world")
+    const result = combine(maybe1, maybe2, (value1, value2) => `${value1} ${value2}`)
+    assert.deepEqual(result, { tag: "Just", value: "hello world" })
+  })
+})
diff --git a/src/shared/utils/typeSafety.test.ts b/src/shared/utils/typeSafety.test.ts
new file mode 100644
index 00000000..98459077
--- /dev/null
+++ b/src/shared/utils/typeSafety.test.ts
@@ -0,0 +1,13 @@
+import assert from "node:assert/strict"
+import { describe, it } from "node:test"
+import { assertExhaustive } from "./typeSafety.ts"
+
+describe("assertExhaustive", () => {
+  it("should throw an error with the message 'The switch is not exhaustive.'", () => {
+    assert.throws(
+      // @ts-expect-error The function should never receive a value.
+      () => assertExhaustive(""),
+      err => err instanceof Error && err.message === "The switch is not exhaustive.",
+    )
+  })
+})