Move kobo auto-suspension logic out of UIManager (#2933)

spec/unit/mock_time_spec.lua

@@ -0,0 +1,52 @@
+describe("MockTime tests", function()
+    teardown(function()
+        require("mock_time"):uninstall()
+    end)
+
+    it("should be able to install and uninstall", function()
+        local mock_time = require("mock_time")
+        local util = require("ffi/util")
+        local current_time = os.time()
+        local current_highres_sec = util.gettime()
+        mock_time:install()
+        assert.is.truthy(mock_time:set(10))
+        assert.are.equal(os.time(), 10)
+        local sec, usec = util.gettime()
+        assert.are.equal(sec, 10)
+        assert.are.equal(usec, 0)
+        mock_time:uninstall()
+        assert.is.truthy(os.time() >= current_time)
+        assert.is.truthy(util.gettime() >= current_highres_sec)
+    end)
+
+    it("should be able to install several times", function()
+        local mock_time = require("mock_time")
+        local util = require("ffi/util")
+        local current_time = os.time()
+        local current_highres_sec = util.gettime()
+        mock_time:install()
+        mock_time:install()
+        mock_time:uninstall()
+        assert.is.truthy(os.time() >= current_time)
+        assert.is.truthy(util.gettime() >= current_highres_sec)
+    end)
+
+    it("should reject invalid value", function()
+        local mock_time = require("mock_time")
+        assert.is.falsy(mock_time:set("100"))
+        assert.is.falsy(mock_time:set(true))
+        assert.is.falsy(mock_time:set(nil))
+        assert.is.falsy(mock_time:set(function() end))
+    end)
+
+    it("should increase time", function()
+        local mock_time = require("mock_time")
+        local current_time = os.time()
+        mock_time:install()
+        assert.is.truthy(mock_time:set(10.1))
+        assert.are.equal(os.time(), 10)
+        mock_time:increase(1)
+        assert.are.equal(os.time(), 11)
+        mock_time:uninstall()
+    end)
+end)