diff --git a/.busted b/.busted
new file mode 100644
index 00000000..ed6f8878
--- /dev/null
+++ b/.busted
@@ -0,0 +1,6 @@
+return {
+  default = {
+    lpath = "./lua/?.lua;./lua/?/init.lua",
+  }
+}
+-- vim: ft=lua
diff --git a/.luacheckrc b/.luacheckrc
index 0da34feb..53fc740e 100644
--- a/.luacheckrc
+++ b/.luacheckrc
@@ -14,6 +14,7 @@ not_globals = {
 include_files = {
   "**/*.lua",
   "*.rockspec",
+  ".busted",
   ".luacheckrc",
 }
 
diff --git a/.travis.yml b/.travis.yml
index cb2bf6d9..32033341 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,11 +16,13 @@ before_install:
   - hererocks here -r^ --$LUA
   - source here/bin/activate
   - luarocks install luacov-coveralls
+  - luarocks install busted
 
 install:
   - luarocks make
 
 script:
+  - busted -c -v
   - lua run.lua tests --luacov
   - lua run.lua examples
 
diff --git a/appveyor.yml b/appveyor.yml
index 6233d941..3bc26dba 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -20,11 +20,13 @@ before_build:
   - call here\bin\activate
   - "if \"%LUA%\"==\"lua 5.4\" ( luarocks install bit32 )"
   - luarocks install luacov-coveralls
+  - luarocks install busted
 
 build_script:
   - luarocks make
 
 test_script:
+  - busted -c -v
   - lua run.lua tests --luacov
   - lua run.lua examples
 
diff --git a/penlight-dev-1.rockspec b/penlight-dev-1.rockspec
index 73246a29..b02570f5 100644
--- a/penlight-dev-1.rockspec
+++ b/penlight-dev-1.rockspec
@@ -26,6 +26,14 @@ dependencies = {
   "luafilesystem"
 }
 
+test_dependencies = {
+  "busted",
+}
+
+test = {
+  type = "busted",
+}
+
 build = {
   type = "builtin",
   modules = {
diff --git a/spec/app_spec.lua b/spec/app_spec.lua
new file mode 100644
index 00000000..3b1f2909
--- /dev/null
+++ b/spec/app_spec.lua
@@ -0,0 +1,27 @@
+local app = require("pl.app")
+
+describe("pl.app.lua", function ()
+
+  local invocation = app.lua()
+
+  it("should pick up the arguments used to run this test", function ()
+    assert.is.truthy(invocation:match("lua.+package.+busted"))
+  end)
+
+  it("should be reusable to invoke Lua", function ()
+    assert.is.truthy(os.execute(app.lua()..' -e "n=1;os.exit(n-1)"'))
+  end)
+
+end)
+
+describe("pl.app.platform", function ()
+
+  -- TODO: Find a reliable alternate way to determine platform to check that
+  -- this is returning the right answer, not just any old answer.
+  it("should at least return a valid platform", function ()
+    local platforms = { Linux = true, OSX = true, Windows = true }
+    local detected = app.platform()
+    assert.is.truthy(platforms[detected])
+  end)
+
+end)
diff --git a/spec/date_spec.lua b/spec/date_spec.lua
new file mode 100644
index 00000000..1032de25
--- /dev/null
+++ b/spec/date_spec.lua
@@ -0,0 +1,48 @@
+local Date = require("pl.Date")
+
+describe("pl.Date", function ()
+
+  describe("function", function ()
+
+    describe("Format()", function ()
+
+      it("should output parsable inputs", function ()
+        local function assert_date_format(expected, format)
+          local df = Date.Format(format)
+          local d = df:parse(expected)
+          assert.is.equal(expected, df:tostring(d))
+        end
+        assert_date_format('02/04/10', 'dd/mm/yy')
+        assert_date_format('04/02/2010', 'mm/dd/yyyy')
+        assert_date_format('2011-02-20', 'yyyy-mm-dd')
+        assert_date_format('20070320', 'yyyymmdd')
+        assert_date_format('23:10', 'HH:MM')
+      end)
+
+      it("should parse 'slack' fields", function ()
+        local df = Date.Format("m/d/yy")
+        -- TODO: Re-enable when issue #359 fixed
+        -- assert.is.equal('01/05/99', df:tostring(df:parse('1/5/99')))
+        assert.is.equal('01/05/01', df:tostring(df:parse('1/5/01')))
+        assert.is.equal('01/05/32', df:tostring(df:parse('1/5/32')))
+      end)
+
+    end)
+
+  end)
+
+  describe("meta method", function ()
+
+    describe("__tostring()", function ()
+
+      it("should be suitable for serialization", function ()
+        local df = Date.Format()
+        local du = df:parse("2008-07-05")
+        assert.is.equal(du, du:toUTC())
+      end)
+
+    end)
+
+  end)
+
+end)
diff --git a/spec/multimap_spec.lua b/spec/multimap_spec.lua
new file mode 100644
index 00000000..a83d1500
--- /dev/null
+++ b/spec/multimap_spec.lua
@@ -0,0 +1,14 @@
+local MultiMap = require("pl.MultiMap")
+
+describe("pl.MultiMap", function ()
+
+  it("should hold multiple values per key", function ()
+    local map = MultiMap()
+    map:set('foo', 1)
+    map:set('bar', 3)
+    map:set('foo', 2)
+    local expected = { foo = { 1, 2 }, bar = { 3 } }
+    assert.is.same(expected, map)
+  end)
+
+end)
diff --git a/spec/pretty_spec.lua b/spec/pretty_spec.lua
new file mode 100644
index 00000000..85e37706
--- /dev/null
+++ b/spec/pretty_spec.lua
@@ -0,0 +1,40 @@
+local pretty = require("pl.pretty")
+
+describe("pl.pretty.number", function ()
+
+  it("should format memory", function ()
+    local function assert_memory (expected, input)
+      assert.is.equal(expected, pretty.number(input, "M"))
+    end
+    assert_memory("123B", 123)
+    assert_memory("1.2KiB", 1234)
+    assert_memory("10.0KiB", 10*1024)
+    assert_memory("1.0MiB", 1024*1024)
+    assert_memory("1.0GiB", 1024*1024*1024)
+  end)
+
+  it("should format postfixes", function ()
+    local function assert_postfix(expected, input)
+      assert.is.equal(expected, pretty.number(input, "N", 2))
+    end
+    assert_postfix("123", 123)
+    assert_postfix("1.23K", 1234)
+    assert_postfix("10.24K", 10*1024)
+    assert_postfix("1.05M", 1024*1024)
+    assert_postfix("1.07B", 1024*1024*1024)
+  end)
+
+  it("should format postfixes", function ()
+    local function assert_separator(expected, input)
+      assert.is.equal(expected, pretty.number(input, "T"))
+    end
+    assert_separator('123', 123)
+    assert_separator('1,234', 1234)
+    assert_separator('12,345', 12345)
+    assert_separator('123,456', 123456)
+    assert_separator('1,234,567', 1234567)
+    assert_separator('12,345,678', 12345678)
+  end)
+
+
+end)
diff --git a/spec/set_spec.lua b/spec/set_spec.lua
new file mode 100644
index 00000000..02febcaa
--- /dev/null
+++ b/spec/set_spec.lua
@@ -0,0 +1,84 @@
+local Set = require("pl.Set")
+
+describe("pl.Set", function ()
+
+  local s = Set()
+  local s1_2 = Set({ 1, 2 })
+  local s1_2_3 = Set({ 1, 2, 3 })
+  local s1_3 = Set({ 1, 3 })
+  local s2 = Set({ 2 })
+  local s2_1 = Set({ 2, 1 })
+  local s2_3 = Set({ 2, 3 })
+  local s3 = Set({ 3 })
+  local sm = Set({ "foo", "bar" })
+
+  it("should produce a set object", function ()
+    assert.is.same({ true, true }, s1_2)
+  end)
+
+  it("should produce identical sets for any ordered input", function ()
+    assert.is.same(s1_2, s2_1)
+  end)
+
+  describe("should have an operator for", function ()
+
+    it("union", function ()
+      assert.is.same(s1_2_3, s1_2 + s3)
+      assert.is.same(s1_2_3, s1_2 + 3)
+    end)
+
+    it("intersection", function ()
+      assert.is.same(s2, s1_2 * s2_3)
+    end)
+
+    it("difference", function ()
+      assert.is.same(s2_1, s1_2_3 - s3)
+      assert.is.same(s2_3, s1_2_3 - 1)
+    end)
+
+    it("symmetric difference", function ()
+      assert.is.same(s1_3, s1_2 ^ s2_3)
+    end)
+
+    it("tostring", function ()
+      -- Cannot test multi-entry sets because of non-deterministic key order
+      assert.is.same('[2]', tostring(s2))
+    end)
+
+  end)
+
+  describe("should provide functions", function ()
+
+    it("isempty", function ()
+      assert.is.truthy(Set.isempty(s))
+      assert.is.falsy(Set.isempty(s3))
+    end)
+
+    it("set", function ()
+      local m = Set()
+      Set.set(m, 'foo', true)
+      m.bar = true
+      assert.is.same(m, sm)
+      assert.is_not.same(m, s1_2)
+    end)
+
+  end)
+
+  describe("should have a comparison operator for", function ()
+
+    it("supersets/subsets than", function ()
+      assert.is.truthy(s1_2 > s2)
+      assert.is.falsy(s1_3 > s2)
+      assert.is.falsy(s1_2 > s2_3)
+      assert.is.truthy(s1_2 < s1_2_3)
+      assert.is.falsy(s1_2_3 < s1_2)
+    end)
+
+    it("equality", function ()
+      assert.is.truthy(s1_2 == s2_1)
+      assert.is.falsy(s1_2 == s2_3)
+    end)
+
+  end)
+
+end)
diff --git a/spec/text_spec.lua b/spec/text_spec.lua
new file mode 100644
index 00000000..cd42f061
--- /dev/null
+++ b/spec/text_spec.lua
@@ -0,0 +1,11 @@
+local text = require("pl.text")
+
+describe("pl.text.Template", function ()
+
+  it("replaces placeholders", function ()
+    local tempalte = text.Template("${here} is the $answer")
+    local out = tempalte:substitute({ here = 'one', answer = 'two' })
+    assert.is.equal('one is the two', out)
+  end)
+
+end)
diff --git a/tests/test-app.lua b/tests/test-app.lua
index 20ce6294..f5066cc2 100644
--- a/tests/test-app.lua
+++ b/tests/test-app.lua
@@ -260,4 +260,3 @@ do -- app.parse_args
     asserteq(s, {})
 
 end
-
diff --git a/tests/test-date.lua b/tests/test-date.lua
index 94bd661a..6a91a098 100644
--- a/tests/test-date.lua
+++ b/tests/test-date.lua
@@ -1,44 +1,10 @@
 local test = require 'pl.test'
-local app = require 'pl.app'
-local utils = require 'pl.utils'
 local asserteq, assertmatch = test.asserteq, test.assertmatch
 local dump = require 'pl.pretty'.dump
 local T = require 'pl.test'.tuple
 
 local Date = require 'pl.Date'
 
---[[
-d = Date()
-print(d)
-print(d:year())
-d:day(20)
-print(d)
-d:add {day = 2}
-print(d:day())
-d = Date() -- 'now'
-print(d:last_day():day())
-print(d:month(7):last_day())
---]]
-
-function check_df(fmt,str,no_check)
-    local df = Date.Format(fmt)
-    local d = df:parse(str)
-    --print(str,d)
-    if not no_check then
-        asserteq(df:tostring(d),str)
-    end
-end
-
-check_df('dd/mm/yy','02/04/10')
-check_df('mm/dd/yyyy','04/02/2010')
-check_df('yyyy-mm-dd','2011-02-20')
-check_df('yyyymmdd','20070320')
-
--- use single fields for 'slack' parsing
-check_df('m/d/yyyy','1/5/2001',true)
-
-check_df('HH:MM','23:10')
-
 iso = Date.Format 'yyyy-mm-dd' -- ISO date
 d = iso:parse '2010-04-10'
 asserteq(T(d:day(),d:month(),d:year()),T(10,4,2010))
@@ -119,10 +85,3 @@ asserteq(tostring(nxt - d), '1 month ')
 --- Can explicitly get UTC date; these of course refer to same time
 local now,utc  = Date(), Date 'utc'
 asserteq(tostring(now - utc),'zero')
-
-if app.platform() ~= 'Windows' then
-    print(app.lua())
-    if not utils.execute ("TZ='Europe/London' "..app.lua().." tests/test-date2.lua") then
-        error "buggered!"
-    end
-end
diff --git a/tests/test-date2.lua b/tests/test-date2.lua
deleted file mode 100644
index 230fb183..00000000
--- a/tests/test-date2.lua
+++ /dev/null
@@ -1,10 +0,0 @@
-local Date = require 'pl.Date'
-local test = require 'pl.test'
-local df = Date.Format()
-local dl = df:parse '2008-07-05'
-local du = dl:toUTC()
-
-test.asserteq(dl,du)
-
-
-
diff --git a/tests/test-multimap.lua b/tests/test-multimap.lua
deleted file mode 100644
index 1cb29258..00000000
--- a/tests/test-multimap.lua
+++ /dev/null
@@ -1,11 +0,0 @@
-local asserteq = require 'pl.test' . asserteq
-local MultiMap = require 'pl.MultiMap'
-
-m = MultiMap()
-m:set('john',1)
-m:set('jane',3)
-m:set('john',2)
-
-local ms = MultiMap{john={1,2},jane={3}}
-
-asserteq(m,ms)
diff --git a/tests/test-pretty-number.lua b/tests/test-pretty-number.lua
deleted file mode 100644
index 347a5cf5..00000000
--- a/tests/test-pretty-number.lua
+++ /dev/null
@@ -1,33 +0,0 @@
-local test = require 'pl.test'
-local pretty = require 'pl.pretty'
-
-function testm(x,s)
-  test.asserteq(pretty.number(x,'M'),s)
-end
-
-testm(123,'123B')
-testm(1234,'1.2KiB')
-testm(10*1024,'10.0KiB')
-testm(1024*1024,'1.0MiB')
-
-function testn(x,s)
-  test.asserteq(pretty.number(x,'N',2),s)
-end
-
-testn(123,'123')
-testn(1234,'1.23K')
-testn(10*1024,'10.24K')
-testn(1024*1024,'1.05M')
-testn(1024*1024*1024,'1.07B')
-
-function testc(x,s)
-  test.asserteq(pretty.number(x,'T'),s)
-end
-
-testc(123,'123')
-testc(1234,'1,234')
-testc(12345,'12,345')
-testc(123456,'123,456')
-testc(1234567,'1,234,567')
-testc(12345678,'12,345,678')
-
diff --git a/tests/test-set.lua b/tests/test-set.lua
deleted file mode 100644
index 6c123217..00000000
--- a/tests/test-set.lua
+++ /dev/null
@@ -1,37 +0,0 @@
-local Set = require 'pl.Set'
-local asserteq = require 'pl.test' . asserteq
-
-local s1 = Set{1,2}
-local s2 = Set{1,2}
--- equality
-asserteq(s1,s2)
--- union
-asserteq(Set{1,2} + Set{2,3},  Set{1,2,3})
-asserteq(Set{1,2} + 3,   Set{1,2,3})
--- intersection
-asserteq(Set{1,2} * Set{2,3},   Set{2})
--- difference
-local fruit = Set{'apple','banana','orange','apricots'}
-local tropical = Set{'banana','orange'}
-
-asserteq(fruit - tropical,  Set{'apple','apricots'})
-asserteq(tropical - 'orange', Set{'banana'})
-
--- symmetric_difference
-asserteq(Set{1,2} ^ Set{2,3}, Set{1,3})
--- tostring - illustrative, because these assertions may or may not work,
--- due to no ordering in set elements
---asserteq(tostring(S{1,2}),'[1,2]')
---asserteq(tostring(S{1,S{2,3}}),'[1,[2,3]]')
-
-local s3 = Set()
-asserteq(Set.isempty(s3),true)
-
-local s4 = Set{1,2,3}
-
--- subsets/supersets
-asserteq(s4 > s1,true)
-
-Set.set(s3,'one',true)
-s3.two = true
-asserteq(s3,Set{'one','two'})
diff --git a/tests/test-text2.lua b/tests/test-text2.lua
deleted file mode 100644
index c22edbe9..00000000
--- a/tests/test-text2.lua
+++ /dev/null
@@ -1,8 +0,0 @@
-local text = require 'pl.text'
-local Template = text.Template
-local asserteq = require 'pl.test' . asserteq
-
-
-local t = Template('${here} is the $answer')
-asserteq(t:substitute {here = 'one', answer = 'two'} , 'one is the two')
-