Support sharding robolectric tests

Explicitly pass the list of tests as LOCAL_ROBOTEST_FILES, and
support sharding the list of tests into multiple test runners.

Also filter out BaseRobolectricTest.java, which covers the only
use of LOCAL_ROBOTEST_FILES in Android.mk files.

Bug: 133878985
Test: m RunSettingsLibRoboTests runs the same number of tests before and after
Test: m RunSettingsLibRoboTests runs the same number of tests when sharded
Change-Id: Id85ffe03c98e722303eaa6def17812ed2244c6a6
Merged-In: Id85ffe03c98e722303eaa6def17812ed2244c6a6

java/robolectric_test.go

@@ -0,0 +1,88 @@
+// Copyright 2019 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package java
+
+import (
+	"reflect"
+	"testing"
+)
+
+func Test_shardTests(t *testing.T) {
+	type args struct {
+		paths  []string
+		shards int
+	}
+	tests := []struct {
+		name string
+		args args
+		want [][]string
+	}{
+		{
+			name: "empty",
+			args: args{
+				paths:  nil,
+				shards: 1,
+			},
+			want: [][]string(nil),
+		},
+		{
+			name: "too many shards",
+			args: args{
+				paths:  []string{"a", "b"},
+				shards: 3,
+			},
+			want: [][]string{{"a"}, {"b"}},
+		},
+		{
+			name: "single shard",
+			args: args{
+				paths:  []string{"a", "b"},
+				shards: 1,
+			},
+			want: [][]string{{"a", "b"}},
+		},
+		{
+			name: "shard per input",
+			args: args{
+				paths:  []string{"a", "b", "c"},
+				shards: 3,
+			},
+			want: [][]string{{"a"}, {"b"}, {"c"}},
+		},
+		{
+			name: "balanced shards",
+			args: args{
+				paths:  []string{"a", "b", "c", "d"},
+				shards: 2,
+			},
+			want: [][]string{{"a", "b"}, {"c", "d"}},
+		},
+		{
+			name: "unbalanced shards",
+			args: args{
+				paths:  []string{"a", "b", "c"},
+				shards: 2,
+			},
+			want: [][]string{{"a", "b"}, {"c"}},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := shardTests(tt.args.paths, tt.args.shards); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("shardTests() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}