types: ConsensusParams test + document the ranges/limits

Fixes https://github.com/tendermint/tendermint/issues/747
Updates https://github.com/tendermint/tendermint/issues/693

* Document the unmentioned limits for ConsensusParams.Validate()
* Make the limit for ConsensusParams.BlockSizeParams.MaxBytes
clear at 100MiB

types/params.go

@@ -5,7 +5,7 @@ import (
 )
 
 const (
-	maxBlockSizeBytes = 104857600 // 100MB
+	_100MiB = 104857600
 )
 
 // ConsensusParams contains consensus critical parameters
@@ -69,6 +69,10 @@ func DefaultBlockGossipParams() BlockGossipParams {
 
 // Validate validates the ConsensusParams to ensure all values
 // are within their allowed limits, and returns an error if they are not.
+// Expecting:
+// * BlockSizeParams.MaxBytes > 0
+// * BlockGossipParams.BlockPartSizeBytes > 0
+// * BlockSizeParams.MaxBytes <= 100MiB
 func (params *ConsensusParams) Validate() error {
 	// ensure some values are greater than 0
 	if params.BlockSizeParams.MaxBytes <= 0 {
@@ -79,9 +83,9 @@ func (params *ConsensusParams) Validate() error {
 	}
 
 	// ensure blocks aren't too big
-	if params.BlockSizeParams.MaxBytes > maxBlockSizeBytes {
+	if params.BlockSizeParams.MaxBytes > _100MiB {
 		return errors.Errorf("BlockSizeParams.MaxBytes is too big. %d > %d",
-			params.BlockSizeParams.MaxBytes, maxBlockSizeBytes)
+			params.BlockSizeParams.MaxBytes, _100MiB)
 	}
 	return nil
 }

types/params_test.go

@@ -0,0 +1,66 @@
+package types_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/tendermint/tendermint/types"
+)
+
+func TestConsensusParamsValidation(t *testing.T) {
+	tests := [...]struct {
+		params  *types.ConsensusParams
+		wantErr string
+	}{
+		{&types.ConsensusParams{}, "BlockSizeParams.MaxBytes must be greater than 0"},
+		{
+			&types.ConsensusParams{BlockSizeParams: types.BlockSizeParams{MaxBytes: 10}},
+			"BlockGossipParams.BlockPartSizeBytes must be greater than 0",
+		},
+		{
+			&types.ConsensusParams{
+				BlockSizeParams:   types.BlockSizeParams{MaxBytes: 10},
+				BlockGossipParams: types.BlockGossipParams{BlockPartSizeBytes: -1},
+			}, "BlockGossipParams.BlockPartSizeBytes must be greater than 0",
+		},
+		{
+			&types.ConsensusParams{
+				BlockSizeParams:   types.BlockSizeParams{MaxBytes: 10},
+				BlockGossipParams: types.BlockGossipParams{BlockPartSizeBytes: 400},
+			}, ""},
+		{
+			&types.ConsensusParams{
+				BlockSizeParams:   types.BlockSizeParams{MaxBytes: 1024 * 1024 * 47},
+				BlockGossipParams: types.BlockGossipParams{BlockPartSizeBytes: 400},
+			}, "",
+		},
+		{
+			&types.ConsensusParams{
+				BlockSizeParams:   types.BlockSizeParams{MaxBytes: 1024 * 1024 * 100},
+				BlockGossipParams: types.BlockGossipParams{BlockPartSizeBytes: 400},
+			}, "",
+		},
+		{
+			&types.ConsensusParams{
+				BlockSizeParams:   types.BlockSizeParams{MaxBytes: 1024 * 1024 * 101},
+				BlockGossipParams: types.BlockGossipParams{BlockPartSizeBytes: 400},
+			}, "BlockSizeParams.MaxBytes is too big",
+		},
+		{
+			&types.ConsensusParams{
+				BlockSizeParams:   types.BlockSizeParams{MaxBytes: 1024 * 1024 * 1024},
+				BlockGossipParams: types.BlockGossipParams{BlockPartSizeBytes: 400},
+			}, "BlockSizeParams.MaxBytes is too big",
+		},
+	}
+
+	for i, tt := range tests {
+		err := tt.params.Validate()
+		if tt.wantErr != "" {
+			assert.Contains(t, err.Error(), tt.wantErr, "#%d: params: %#v", i, tt.params)
+		} else {
+			assert.Nil(t, err, "#%d: want nil error; Params: %#v", i, tt.params)
+		}
+	}
+}