test: an unknown PIXA_ environment variable aborts startup (closes #133)

Tests, written before the change, for the check of PIXA_ names at
startup: a PIXA_ variable that is not a setting's variable aborts naming
it, PIXA_PORT aborts with a message saying to use PORT, and
PIXA_CONFIG_PATH and every setting's variable are accepted. They call
validateKnownEnvVars, which the change adds, so the package does not
build until it lands.

Model: opus-5-5

internal/config/env_internal_test.go

@@ -95,6 +95,43 @@ func TestEnvironmentSetsEveryKey(t *testing.T) {
 	}
 }
 
+// TestUnknownPixaVariableAbortsStartup checks that a PIXA_ variable that
+// is not a setting's variable, such as a misspelled one, aborts startup
+// naming it, as an unknown config key does, instead of being ignored.
+func TestUnknownPixaVariableAbortsStartup(t *testing.T) {
+	t.Setenv("PIXA_TRUSTED_PROXY", "192.0.2.0/24")
+	t.Setenv("PIXA_SIGNINGKEY", validTestSigningKey)
+
+	err := validateKnownEnvVars()
+	wantStartupError(t, err, "PIXA_TRUSTED_PROXY", "PIXA_SIGNINGKEY")
+}
+
+// TestPixaPortAbortsStartupPointingToPort checks that PIXA_PORT aborts
+// startup with a message saying to use PORT, which sets the port.
+func TestPixaPortAbortsStartupPointingToPort(t *testing.T) {
+	t.Setenv("PIXA_PORT", "9090")
+
+	err := validateKnownEnvVars()
+	wantStartupError(t, err, "PIXA_PORT", "use PORT")
+}
+
+// TestSettingVariablesAndConfigPathAreAccepted checks that every
+// setting's variable and PIXA_CONFIG_PATH pass the check for unknown
+// PIXA_ variables. TestEnvironmentSetsEveryKey pins the names in the list.
+func TestSettingVariablesAndConfigPathAreAccepted(t *testing.T) {
+	t.Setenv("PIXA_CONFIG_PATH", "/etc/pixa/config.yml")
+
+	for _, name := range envVarNames() {
+		t.Setenv(name, "")
+	}
+
+	err := validateKnownEnvVars()
+	if err != nil {
+		t.Fatalf("PIXA_CONFIG_PATH and every setting's variable "+
+			"must be accepted: %v", err)
+	}
+}
+
 // TestPortFromEnvironmentOverridesConfigFile checks that PORT wins over
 // the port in the config file.
 func TestPortFromEnvironmentOverridesConfigFile(t *testing.T) {