hash/maphash: add more tests for seed generation

Test all the paths by which a Hash picks its seed.
Make sure they all behave identically to a preset seed.

Change-Id: I2f7950857697f2f07226b96655574c36931b2aae
Reviewed-on: https://go-review.googlesource.com/c/go/+/220686
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Vladimir Evgrafov <evgrafov.vladimir@gmail.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

1 files changed, 56 insertions, 0 deletions

diff --git a/src/hash/maphash/maphash_test.go b/src/hash/maphash/maphash_test.go
index 0164a9e20a..caea43a8c8 100644
--- a/src/hash/maphash/maphash_test.go
+++ b/src/hash/maphash/maphash_test.go
@@ -106,6 +106,62 @@ func TestRepeat(t *testing.T) {
 	}
 }
 
+func TestSeedFromSum64(t *testing.T) {
+	h1 := new(Hash)
+	h1.WriteString("foo")
+	x := h1.Sum64() // seed generated here
+	h2 := new(Hash)
+	h2.SetSeed(h1.Seed())
+	h2.WriteString("foo")
+	y := h2.Sum64()
+	if x != y {
+		t.Errorf("hashes don't match: want %x, got %x", x, y)
+	}
+}
+
+func TestSeedFromSeed(t *testing.T) {
+	h1 := new(Hash)
+	h1.WriteString("foo")
+	_ = h1.Seed() // seed generated here
+	x := h1.Sum64()
+	h2 := new(Hash)
+	h2.SetSeed(h1.Seed())
+	h2.WriteString("foo")
+	y := h2.Sum64()
+	if x != y {
+		t.Errorf("hashes don't match: want %x, got %x", x, y)
+	}
+}
+
+func TestSeedFromFlush(t *testing.T) {
+	b := make([]byte, 65)
+	h1 := new(Hash)
+	h1.Write(b) // seed generated here
+	x := h1.Sum64()
+	h2 := new(Hash)
+	h2.SetSeed(h1.Seed())
+	h2.Write(b)
+	y := h2.Sum64()
+	if x != y {
+		t.Errorf("hashes don't match: want %x, got %x", x, y)
+	}
+}
+
+func TestSeedFromReset(t *testing.T) {
+	h1 := new(Hash)
+	h1.WriteString("foo")
+	h1.Reset() // seed generated here
+	h1.WriteString("foo")
+	x := h1.Sum64()
+	h2 := new(Hash)
+	h2.SetSeed(h1.Seed())
+	h2.WriteString("foo")
+	y := h2.Sum64()
+	if x != y {
+		t.Errorf("hashes don't match: want %x, got %x", x, y)
+	}
+}
+
 // Make sure a Hash implements the hash.Hash and hash.Hash64 interfaces.
 var _ hash.Hash = &Hash{}
 var _ hash.Hash64 = &Hash{}