Add more tests (#253)

I'm not entirely sure how useful all of these will be yet - still
trying to work out what/when to test things, but hopefully this'll
be a useful datapoint.

src/test/resources/test-rom/spec/programs/alias_spec.lua

@@ -0,0 +1,28 @@
+local capture = require "test_helpers".capture_program
+
+describe("The alias program", function()
+    it("displays its usage when given too many arguments", function()
+        expect(capture(stub, "alias a b c"))
+            :matches { ok = true, output = "Usage: alias <alias> <program>\n", error = "" }
+    end)
+
+    it("lists aliases", function()
+        local pagedTabulate = stub(textutils, "pagedTabulate", function(x) print(table.unpack(x)) end)
+        stub(shell, "aliases", function() return { cp = "copy" } end)
+        expect(capture(stub, "alias"))
+            :matches { ok = true, output = "cp:copy\n", error = "" }
+        expect(pagedTabulate):called_with_matching({ "cp:copy" })
+    end)
+
+    it("sets an alias", function()
+        local setAlias = stub(shell, "setAlias")
+        capture(stub, "alias test Hello")
+        expect(setAlias):called_with("test", "Hello")
+    end)
+
+    it("clears an alias", function()
+        local clearAlias = stub(shell, "clearAlias")
+        capture(stub, "alias test")
+        expect(clearAlias):called_with("test")
+    end)
+end)