Merge pull request #29 from buildkite/windows-env-flake

fix: Env test flakes on Windows

internal/env/env.go

@@ -20,6 +20,9 @@ func CaseSensitive(actuallyCaseSensitive bool) Options {
 // FromMap is an option that sets the Env to have the key-values pairs from the `source` map.
 // The key-value pair will be inserted with the case sensitivity of the Env, which by default is
 // case-insensitive on Windows and case-sensitive on other platforms.
+// Note that random map iteration will cause the result to be non-deterministic if there are
+// multiple keys in `source`, which are equivalent under case insensitivity, that have different
+// corresponding values.
 func FromMap(source map[string]string) Options {
 	return func(e *Env) {
 		if e.env == nil {

internal/env/env_test.go

@@ -50,7 +50,36 @@ func TestEnvCaseInsensitive(t *testing.T) {
 func TestEnvWithMap(t *testing.T) {
 	t.Parallel()
 
-	e := env.New(env.FromMap(map[string]string{"FOO": "upper-bar", "Foo": "lower-bar"}))
+	// To prevent this test from flaking on Windows, the `source` map should not
+	// contain case-insensitively-equivalent keys with different values.
+
+	e := env.New(env.FromMap(map[string]string{"FOO": "foo", "Bar": "bar"}))
+
+	if v, found := e.Get("FOO"); !found {
+		expected := "foo"
+		if v != expected {
+			t.Errorf("Expected FOO to be %q, got %q", expected, v)
+		}
+	}
+
+	if v, found := e.Get("Bar"); !found || v != "bar" {
+		t.Errorf(`Expected Foo to be "bar", got %q`, v)
+	}
+
+	if _, found := e.Get("not-foo"); found {
+		t.Errorf("Expected not-foo to not be found")
+	}
+}
+
+func TestEnvDefaults(t *testing.T) {
+	t.Parallel()
+
+	// To prevent this test from flaking on Windows, e should not be created
+	// with FromMap.
+
+	e := env.New()
+	e.Set("FOO", "upper-bar")
+	e.Set("Foo", "lower-bar")
 
 	if v, found := e.Get("FOO"); !found {
 		expected := "upper-bar"