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/label_spec.lua

@@ -0,0 +1,34 @@
+local capture = require "test_helpers".capture_program
+
+describe("The label program", function()
+    it("displays its usage when given no arguments", function()
+        expect(capture(stub, "label"))
+            :matches { ok = true, output = "Usages:\nlabel get\nlabel get <drive>\nlabel set <text>\nlabel set <drive> <text>\nlabel clear\nlabel clear <drive>\n", error = "" }
+    end)
+
+    describe("displays the computer's label", function()
+        it("when it is not labelled", function()
+            stub(os, "getComputerLabel", function() return nil end)
+            expect(capture(stub, "label get"))
+                :matches { ok = true, output = "No Computer label\n", error = "" }
+        end)
+
+        it("when it is labelled", function()
+            stub(os, "getComputerLabel", function() return "Test" end)
+            expect(capture(stub, "label get"))
+                :matches { ok = true, output = "Computer label is \"Test\"\n", error = "" }
+        end)
+    end)
+
+    it("sets the computer's label", function()
+        local setComputerLabel = stub(os, "setComputerLabel")
+        capture(stub, "label set Test")
+        expect(setComputerLabel):called_with("Test")
+    end)
+
+    it("clears the computer's label", function()
+        local setComputerLabel = stub(os, "setComputerLabel")
+        capture(stub, "label clear")
+        expect(setComputerLabel):called_with(nil)
+    end)
+end)