Write FIFO cache unit tests (#1201)

* write FIFO cache unit tests

* invert expected / actual

* add limit parameter and cache fail on 0 size

* simplify test table and create new test for empty cache

* simpler tests by having a limit of 2

* fix test cases

* typos

* backout uselesss change

* add a "not an LRU" test case

* use switch in fifo unit tests

internal/cache/fifo_test.go

@@ -0,0 +1,208 @@
+// Copyright (C) 2023, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package cache
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestFIFOCacheInsertion(t *testing.T) {
+	type put struct {
+		kv     int
+		exists bool
+	}
+
+	type get struct {
+		k  int
+		ok bool
+	}
+
+	tests := []struct {
+		name string
+		ops  []interface{}
+	}{
+		{
+			name: "inserting up to limit works",
+			ops: []interface{}{
+				put{
+					kv:     0,
+					exists: false,
+				},
+				put{
+					kv:     1,
+					exists: false,
+				},
+			},
+		},
+		{
+			name: "inserting after limit cleans first",
+			ops: []interface{}{
+				put{
+					kv:     0,
+					exists: false,
+				},
+				put{
+					kv:     1,
+					exists: false,
+				},
+				put{
+					kv:     2,
+					exists: false,
+				},
+				get{
+					k:  0,
+					ok: false,
+				},
+			},
+		},
+		{
+			name: "no element removed when cache is exactly full",
+			ops: []interface{}{
+				put{
+					kv:     0,
+					exists: false,
+				},
+				put{
+					kv:     1,
+					exists: false,
+				},
+				get{
+					k:  0,
+					ok: true,
+				},
+				get{
+					k:  1,
+					ok: true,
+				},
+			},
+		},
+		{
+			name: "no element removed when the cache is less than full",
+			ops: []interface{}{
+				put{
+					kv:     0,
+					exists: false,
+				},
+				get{
+					k:  0,
+					ok: true,
+				},
+			},
+		},
+		{
+			name: "inserting existing value when full doesn't free value",
+			ops: []interface{}{
+				put{
+					kv:     0,
+					exists: false,
+				},
+				put{
+					kv:     1,
+					exists: false,
+				},
+				put{
+					kv:     0,
+					exists: true,
+				},
+				get{
+					k:  0,
+					ok: true,
+				},
+			},
+		},
+		{
+			name: "elements removed in FIFO order when cache overfills",
+			ops: []interface{}{
+				put{
+					kv:     0,
+					exists: false,
+				},
+				put{
+					kv:     1,
+					exists: false,
+				},
+				put{
+					kv:     2,
+					exists: false,
+				},
+				get{
+					k:  0,
+					ok: false,
+				},
+				put{
+					kv:     3,
+					exists: false,
+				},
+				get{
+					k:  1,
+					ok: false,
+				},
+			},
+		},
+		{
+			name: "elements removed in FIFO order and not LRU",
+			ops: []interface{}{
+				put{
+					kv:     0,
+					exists: false,
+				},
+				put{
+					kv:     1,
+					exists: false,
+				},
+				put{
+					kv:     0,
+					exists: true,
+				},
+				get{
+					k:  0,
+					ok: true,
+				},
+				put{
+					kv:     2,
+					exists: false,
+				},
+				get{
+					k:  0,
+					ok: false,
+				},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			require := require.New(t)
+
+			cache, err := NewFIFO[int, int](2)
+			require.NoError(err)
+
+			for _, opIntf := range tt.ops {
+				switch op := opIntf.(type) {
+				case put:
+					exists := cache.Put(op.kv, op.kv)
+					require.Equal(op.exists, exists)
+				case get:
+					val, ok := cache.Get(op.k)
+					require.Equal(op.ok, ok)
+					if ok {
+						require.Equal(op.k, val)
+					}
+				default:
+					require.Fail("op can only be a put or a get")
+				}
+			}
+		})
+	}
+}
+
+func TestEmptyCacheFails(t *testing.T) {
+	require := require.New(t)
+	_, err := NewFIFO[int, int](0)
+	expectedErr := errors.New("maxSize must be greater than 0")
+	require.Equal(expectedErr, err)
+}