feat: Mock SystemTime::now() for the tests

Add a fake `struct SystemTime` for mocking `SystemTime::now()` etc. for test purposes. One still
needs to use `std::time::SystemTime` as a struct representing a system time. I think such a
minimalistic approach is ok -- even if somebody uses the original `SystemTime::elapsed()` or `now()`
instead of mocks by mistake, that could break only tests but not the program itself. The worst thing
that can happen is that tests using `SystemTime::shift()` and checking messages timestamps
f.e. wouldn't catch the corresponding bugs, but now we don't have such tests at all which is much
worse.

src/chat.rs

@@ -6,7 +6,7 @@ use std::convert::{TryFrom, TryInto};
 use std::fmt;
 use std::path::{Path, PathBuf};
 use std::str::FromStr;
-use std::time::{Duration, SystemTime};
+use std::time::Duration;
 
 use anyhow::{anyhow, bail, ensure, Context as _, Result};
 use deltachat_derive::{FromSql, ToSql};
@@ -44,7 +44,7 @@ use crate::sync::{self, Sync::*, SyncData};
 use crate::tools::{
     buf_compress, create_id, create_outgoing_rfc724_mid, create_smeared_timestamp,
     create_smeared_timestamps, get_abs_path, gm2local_offset, improve_single_line_input,
-    smeared_time, strip_rtlo_characters, time, IsNoneOrEmpty,
+    smeared_time, strip_rtlo_characters, time, IsNoneOrEmpty, SystemTime,
 };
 use crate::webxdc::WEBXDC_SUFFIX;
 
@@ -3637,7 +3637,7 @@ pub enum MuteDuration {
     Forever,
 
     /// Chat is muted for a limited period of time.
-    Until(SystemTime),
+    Until(std::time::SystemTime),
 }
 
 impl rusqlite::types::ToSql for MuteDuration {

src/contact.rs

@@ -6,7 +6,7 @@ use std::convert::{TryFrom, TryInto};
 use std::fmt;
 use std::ops::Deref;
 use std::path::{Path, PathBuf};
-use std::time::{SystemTime, UNIX_EPOCH};
+use std::time::UNIX_EPOCH;
 
 use anyhow::{bail, ensure, Context as _, Result};
 use async_channel::{self as channel, Receiver, Sender};
@@ -35,7 +35,7 @@ use crate::sql::{self, params_iter};
 use crate::sync::{self, Sync::*, SyncData};
 use crate::tools::{
     duration_to_str, get_abs_path, improve_single_line_input, strip_rtlo_characters, time,
-    EmailAddress,
+    EmailAddress, SystemTime,
 };
 use crate::{chat, stock_str};
 

src/context.rs

@@ -1051,7 +1051,7 @@ pub fn get_version_str() -> &'static str {
 
 #[cfg(test)]
 mod tests {
-    use std::time::{Duration, SystemTime};
+    use std::time::Duration;
 
     use anyhow::Context as _;
     use strum::IntoEnumIterator;
@@ -1067,7 +1067,7 @@ mod tests {
     use crate::message::{Message, Viewtype};
     use crate::receive_imf::receive_imf;
     use crate::test_utils::TestContext;
-    use crate::tools::create_outgoing_rfc724_mid;
+    use crate::tools::{create_outgoing_rfc724_mid, SystemTime};
 
     #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
     async fn test_wrong_db() -> Result<()> {

src/ephemeral.rs

@@ -67,7 +67,7 @@ use std::collections::BTreeSet;
 use std::convert::{TryFrom, TryInto};
 use std::num::ParseIntError;
 use std::str::FromStr;
-use std::time::{Duration, SystemTime, UNIX_EPOCH};
+use std::time::{Duration, UNIX_EPOCH};
 
 use anyhow::{ensure, Result};
 use async_channel::Receiver;
@@ -85,7 +85,7 @@ use crate::message::{Message, MessageState, MsgId, Viewtype};
 use crate::mimeparser::SystemMessage;
 use crate::sql::{self, params_iter};
 use crate::stock_str;
-use crate::tools::{duration_to_str, time};
+use crate::tools::{duration_to_str, time, SystemTime};
 
 /// Ephemeral timer value.
 #[derive(Debug, PartialEq, Eq, Copy, Clone, Serialize, Deserialize)]

src/sql.rs

@@ -21,7 +21,7 @@ use crate::message::{Message, MsgId, Viewtype};
 use crate::param::{Param, Params};
 use crate::peerstate::{deduplicate_peerstates, Peerstate};
 use crate::stock_str;
-use crate::tools::{delete_file, time};
+use crate::tools::{delete_file, time, SystemTime};
 
 /// Extension to [`rusqlite::ToSql`] trait
 /// which also includes [`Send`] and [`Sync`].
@@ -857,9 +857,9 @@ pub async fn remove_unused_files(context: &Context) -> Result<()> {
             Ok(mut dir_handle) => {
                 /* avoid deletion of files that are just created to build a message object */
                 let diff = std::time::Duration::from_secs(60 * 60);
-                let keep_files_newer_than = std::time::SystemTime::now()
+                let keep_files_newer_than = SystemTime::now()
                     .checked_sub(diff)
-                    .unwrap_or(std::time::SystemTime::UNIX_EPOCH);
+                    .unwrap_or(SystemTime::UNIX_EPOCH);
 
                 while let Ok(Some(entry)) = dir_handle.next_entry().await {
                     let name_f = entry.file_name();

src/sync.rs

@@ -319,7 +319,7 @@ impl Context {
 
 #[cfg(test)]
 mod tests {
-    use std::time::{Duration, SystemTime};
+    use std::time::Duration;
 
     use anyhow::bail;
 
@@ -329,6 +329,7 @@ mod tests {
     use crate::contact::{Contact, Origin};
     use crate::test_utils::TestContext;
     use crate::token::Namespace;
+    use crate::tools::SystemTime;
 
     #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
     async fn test_config_sync_msgs() -> Result<()> {

src/timesmearing.rs

@@ -79,11 +79,11 @@ impl SmearedTimestamp {
 
 #[cfg(test)]
 mod tests {
-    use std::time::SystemTime;
-
     use super::*;
     use crate::test_utils::TestContext;
-    use crate::tools::{create_smeared_timestamp, create_smeared_timestamps, smeared_time, time};
+    use crate::tools::{
+        create_smeared_timestamp, create_smeared_timestamps, smeared_time, time, SystemTime,
+    };
 
     #[test]
     fn test_smeared_timestamp() {

src/tools.rs

@@ -9,11 +9,13 @@ use std::io::{Cursor, Write};
 use std::mem;
 use std::path::{Path, PathBuf};
 use std::str::from_utf8;
+#[cfg(test)]
+use std::sync::RwLock;
 // `std::time::Instant` may use `libc::clock_gettime(CLOCK_MONOTONIC)`, e.g. on Android, and does
 // not advance while being in deep sleep mode, so use `SystemTime` for now. When the issue on
 // Android will be solved, we can switch to the true `Instant` easily.
 pub use std::time::SystemTime as Instant;
-use std::time::{Duration, SystemTime};
+use std::time::{Duration, SystemTimeError};
 
 use anyhow::{bail, Context as _, Result};
 use base64::Engine as _;
@@ -479,6 +481,35 @@ pub async fn read_dir(path: &Path) -> Result<Vec<fs::DirEntry>> {
     Ok(res)
 }
 
+#[cfg(test)]
+static SYSTEM_TIME_SHIFT: RwLock<Duration> = RwLock::new(Duration::new(0, 0));
+
+/// Fake struct for mocking `SystemTime::now()` etc. for test purposes. You still need to use
+/// `std::time::SystemTime` as a struct representing a system time.
+pub(crate) struct SystemTime();
+
+impl SystemTime {
+    pub const UNIX_EPOCH: std::time::SystemTime = std::time::SystemTime::UNIX_EPOCH;
+
+    #[allow(unused)]
+    pub fn elapsed(t: &std::time::SystemTime) -> Result<Duration, SystemTimeError> {
+        Self::now().duration_since(*t)
+    }
+
+    pub fn now() -> std::time::SystemTime {
+        #[cfg(not(test))]
+        return std::time::SystemTime::now();
+        #[cfg(test)]
+        return std::time::SystemTime::now() + *SYSTEM_TIME_SHIFT.read().unwrap();
+    }
+
+    /// Simulates a system clock forward adjustment by `duration`.
+    #[cfg(test)]
+    pub fn shift(duration: Duration) {
+        *SYSTEM_TIME_SHIFT.write().unwrap() += duration;
+    }
+}
+
 pub(crate) fn time() -> i64 {
     SystemTime::now()
         .duration_since(SystemTime::UNIX_EPOCH)