Add tests for seed distribution.

tests/Main.elm

@@ -9,7 +9,11 @@ Note that this always uses an initial seed of 902101337, since it can't do effec
 -}
 
 import Platform
+import Random.Pcg as Random
 import Runner.Log
+import Runner.String exposing (Summary)
+import SeedTests
+import Test exposing (Test)
 import Tests
 
 
@@ -21,3 +25,45 @@ main =
         , subscriptions = \_ -> Sub.none
         }
         |> Runner.Log.run Tests.all
+        -- All seed tests should pass because they receive the same initial seed.
+        |> runAllTests 1 SeedTests.fixedSeed SeedTests.tests
+
+
+runAllTests : Int -> Random.Seed -> List Test -> a -> a
+runAllTests runs seed tests =
+    tests
+        |> List.foldl
+            (\test summary ->
+                Runner.String.runWithOptions runs seed test
+                    |> combineSummaries summary
+            )
+            emptySummary
+        |> Runner.Log.logOutput
+
+
+emptySummary : Summary
+emptySummary =
+    { output = "", passed = 0, failed = 0, autoFail = Nothing }
+
+
+combineSummaries : Summary -> Summary -> Summary
+combineSummaries first second =
+    { output = first.output ++ second.output
+    , passed = first.passed + second.passed
+    , failed = first.failed + second.failed
+    , autoFail =
+        case ( first.autoFail, second.autoFail ) of
+            ( Nothing, Nothing ) ->
+                Nothing
+
+            ( Nothing, second ) ->
+                second
+
+            ( first, Nothing ) ->
+                first
+
+            ( Just first, Just second ) ->
+                [ first, second ]
+                    |> String.join "\n"
+                    |> Just
+    }

tests/Runner/Log.elm

@@ -1,4 +1,4 @@
-module Runner.Log exposing (run, runWithOptions)
+module Runner.Log exposing (logOutput, run, runWithOptions)
 
 {-| Log Runner
 

tests/SeedTests.elm

@@ -0,0 +1,72 @@
+module SeedTests exposing (fixedSeed, tests)
+
+import Expect exposing (FloatingPointTolerance(Absolute, AbsoluteOrRelative, Relative))
+import Fuzz exposing (..)
+import Random.Pcg as Random
+import Test exposing (..)
+
+
+fixedSeed : Random.Seed
+fixedSeed =
+    Random.initialSeed 133742
+
+
+expectedNum : Int
+expectedNum =
+    1083264770
+
+
+{-| Most of the tests will use this, but we won't run it directly.
+
+When these tests are run using fixedSeed and a run count of 1, this is the
+exact number they will get when the description around this fuzz test is
+exactly the string "Seed test".
+
+-}
+fuzzTest : Test
+fuzzTest =
+    fuzz int "It receives the expected number" <|
+        \num ->
+            Expect.equal num expectedNum
+
+
+tests : List Test
+tests =
+    [ describe "Seed test"
+        [ fuzzTest ]
+    , describe "Seed test"
+        [ fuzz int "It receives the expected number even though this text is different" <|
+            \num ->
+                Expect.equal num expectedNum
+        ]
+    , describe "Seed test"
+        [ describe "Nested describes shouldn't affect seed distribution"
+            [ fuzzTest ]
+        ]
+    , describe "Seed test"
+        [ test "Unit tests before should not affect seed distribution" <|
+            \_ ->
+                Expect.pass
+        , fuzzTest
+        , test "Unit tests after should not affect seed distribution" <|
+            \_ ->
+                Expect.pass
+        ]
+    , -- Wrapping in a Test.concat shouldn't change anything
+      Test.concat
+        [ describe "Seed test"
+            [ fuzzTest ]
+        ]
+    , -- Wrapping in a Test.concat wth unit tests shouldn't change anything
+      Test.concat
+        [ describe "Seed test"
+            [ test "Unit tests before should not affect seed distribution" <|
+                \_ ->
+                    Expect.pass
+            , fuzzTest
+            , test "Unit tests after should not affect seed distribution" <|
+                \_ ->
+                    Expect.pass
+            ]
+        ]
+    ]