diff --git a/cli/Cargo.toml b/cli/Cargo.toml
index 92fc58208f38c6..87b8df5f275667 100644
--- a/cli/Cargo.toml
+++ b/cli/Cargo.toml
@@ -64,6 +64,7 @@ walkdir = "2.3.1"
 warp = "0.2.2"
 semver-parser = "0.9.0"
 uuid = { version = "0.8.1", features = ["v4"] }
+tokio-tungstenite = { version = "0.10.1", features = ["connect"] }
 
 [target.'cfg(windows)'.dependencies]
 winapi = "0.3.8"
@@ -75,7 +76,7 @@ nix = "0.17.0"
 [dev-dependencies]
 os_pipe = "0.9.1"
 # Used for testing inspector. Keep in-sync with warp.
-tokio-tungstenite = { version = "0.10.1", features = ["connect"] }
+# tokio-tungstenite = { version = "0.10.1", features = ["connect"] }
 
 [target.'cfg(unix)'.dev-dependencies]
 pty = "0.2.2"
diff --git a/cli/coverage.rs b/cli/coverage.rs
new file mode 100644
index 00000000000000..1c03bebc4d5206
--- /dev/null
+++ b/cli/coverage.rs
@@ -0,0 +1,130 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+
+#![allow(unused)]
+
+use crate::futures::SinkExt;
+use crate::futures::StreamExt;
+use crate::tokio_util;
+use deno_core::ErrBox;
+use serde::Deserialize;
+use std;
+use tokio_tungstenite;
+use url::Url;
+
+pub struct CoverageCollector {
+  msg_id: usize,
+  socket: tokio_tungstenite::WebSocketStream<tokio::net::TcpStream>,
+}
+
+impl CoverageCollector {
+  pub async fn connect(url: Url) -> Result<Self, ErrBox> {
+    let (socket, response) = tokio_tungstenite::connect_async(url)
+      .await
+      .expect("Can't connect");
+    assert_eq!(response.status(), 101);
+
+    let mut collector = Self { msg_id: 1, socket };
+
+    eprintln!("start");
+    collector
+      .socket
+      .send(r#"{"id":1,"method":"Runtime.enable"}"#.into())
+      .await
+      .unwrap();
+    collector
+      .socket
+      .send(r#"{"id":2,"method":"Profiler.enable"}"#.into())
+      .await
+      .unwrap();
+    collector.socket.send(r#"{"id":3,"method":"Profiler.startPreciseCoverage", "params": {"callCount": false, "detailed": true } }"#.into()).await.unwrap();
+    collector
+      .socket
+      .send(r#"{"id":4,"method":"Runtime.runIfWaitingForDebugger" }"#.into())
+      .await
+      .unwrap();
+    eprintln!("start1");
+
+    Ok(collector)
+  }
+
+  pub async fn stop_collecting(&mut self) -> Result<(), ErrBox> {
+    let msg = self.socket.next().await.unwrap();
+    dbg!(msg);
+    let msg = self.socket.next().await.unwrap();
+    eprintln!("start2");
+    dbg!(msg);
+    let msg = self.socket.next().await.unwrap();
+    dbg!(msg);
+    let msg = self.socket.next().await.unwrap();
+    dbg!(msg);
+    let msg = self.socket.next().await.unwrap();
+    dbg!(msg);
+
+    self
+      .socket
+      .send(r#"{"id":5,"method":"Profiler.takePreciseCoverage" }"#.into())
+      .await
+      .unwrap();
+    self
+      .socket
+      .send(r#"{"id":6,"method":"Profiler.stopPreciseCoverage" }"#.into())
+      .await
+      .unwrap();
+    Ok(())
+  }
+
+  pub async fn get_report(&mut self) -> Result<Vec<CoverageResult>, ErrBox> {
+    dbg!("before recv");
+    let msg = self.socket.next().await.unwrap();
+    dbg!("after recv");
+    let msg = msg.unwrap();
+    let msg_text = msg.to_text()?;
+
+    let coverage_result: CoverageResultMsg =
+      serde_json::from_str(msg_text).unwrap();
+    // eprintln!("cover result {:#?}", coverage_result);
+
+    // dbg!(msg);
+    let msg = self.socket.next().await.unwrap();
+    dbg!(msg);
+
+    Ok(coverage_result.result.result)
+  }
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct CoverageRange {
+  pub start_offset: usize,
+  pub end_offset: usize,
+  pub count: usize,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct FunctionCoverageResult {
+  pub function_name: String,
+  pub ranges: Vec<CoverageRange>,
+  pub is_block_coverage: bool,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct CoverageResult {
+  pub script_id: String,
+  pub url: String,
+  pub functions: Vec<FunctionCoverageResult>,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(rename_all = "camelCase")]
+struct Res {
+  result: Vec<CoverageResult>,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(rename_all = "camelCase")]
+struct CoverageResultMsg {
+  id: usize,
+  result: Res,
+}
diff --git a/cli/flags.rs b/cli/flags.rs
index 772c719a8849b7..75ac50e2760183 100644
--- a/cli/flags.rs
+++ b/cli/flags.rs
@@ -68,6 +68,7 @@ pub enum DenoSubcommand {
     allow_none: bool,
     include: Option<Vec<String>>,
     filter: Option<String>,
+    coverage: bool,
   },
   Types,
   Upgrade {
@@ -541,6 +542,7 @@ fn test_parse(flags: &mut Flags, matches: &clap::ArgMatches) {
 
   let failfast = matches.is_present("failfast");
   let allow_none = matches.is_present("allow_none");
+  let coverage = matches.is_present("coverage");
   let filter = matches.value_of("filter").map(String::from);
   let include = if matches.is_present("files") {
     let files: Vec<String> = matches
@@ -558,6 +560,7 @@ fn test_parse(flags: &mut Flags, matches: &clap::ArgMatches) {
     include,
     filter,
     allow_none,
+    coverage,
   };
 }
 
@@ -975,6 +978,11 @@ fn test_subcommand<'a, 'b>() -> App<'a, 'b> {
         .takes_value(true)
         .help("A pattern to filter the tests to run by"),
     )
+    .arg(
+      Arg::with_name("coverage")
+        .long("coverage")
+        .help("Collect coverage information, requires --inspect flag"),
+    )
     .arg(
       Arg::with_name("files")
         .help("List of file names to run")
@@ -2303,6 +2311,7 @@ mod tests {
           filter: None,
           allow_none: true,
           include: Some(svec!["dir1/", "dir2/"]),
+          coverage: false,
         },
         allow_read: true,
         allow_net: true,
@@ -2322,6 +2331,7 @@ mod tests {
           allow_none: false,
           filter: Some("foo".to_string()),
           include: Some(svec!["dir1"]),
+          coverage: false,
         },
         allow_read: true,
         ..Flags::default()
diff --git a/cli/lib.rs b/cli/lib.rs
index 467c05708ff325..9f2e654b66e080 100644
--- a/cli/lib.rs
+++ b/cli/lib.rs
@@ -24,6 +24,7 @@ extern crate url;
 mod checksum;
 pub mod colors;
 pub mod compilers;
+mod coverage;
 pub mod deno_dir;
 pub mod diagnostics;
 mod disk_cache;
@@ -66,6 +67,8 @@ pub use dprint_plugin_typescript::swc_ecma_ast;
 pub use dprint_plugin_typescript::swc_ecma_parser;
 
 use crate::compilers::TargetLib;
+use crate::coverage::CoverageCollector;
+use crate::coverage::CoverageResult;
 use crate::doc::parser::DocFileLoader;
 use crate::file_fetcher::SourceFile;
 use crate::file_fetcher::SourceFileFetcher;
@@ -482,6 +485,7 @@ async fn test_command(
   fail_fast: bool,
   allow_none: bool,
   filter: Option<String>,
+  coverage: bool,
 ) -> Result<(), ErrBox> {
   let global_state = GlobalState::new(flags.clone())?;
   let cwd = std::env::current_dir().expect("No current directory");
@@ -500,11 +504,18 @@ async fn test_command(
   let test_file_url =
     Url::from_file_path(&test_file_path).expect("Should be valid file url");
   let test_file =
-    test_runner::render_test_file(test_modules, fail_fast, filter);
+    test_runner::render_test_file(test_modules.clone(), fail_fast, filter);
   let main_module =
     ModuleSpecifier::resolve_url(&test_file_url.to_string()).unwrap();
+
+  // TODO(bartlomieju):
+  // * for --coverage create new `tokio_tungstenite` connection here,
+  // probably on separate thread
+  // * ensure that --inspect flag is on so inspector is available
+
   let mut worker =
     create_main_worker(global_state.clone(), main_module.clone())?;
+
   // Create a dummy source file.
   let source_file = SourceFile {
     filename: test_file_url.to_file_path().unwrap(),
@@ -521,11 +532,61 @@ async fn test_command(
     .global_state
     .file_fetcher
     .save_source_file_in_cache(&main_module, source_file);
+
+  // TODO: * start collecting coverage
+  // coverage_collector.start_collecting();
+  let mut maybe_coverage_collector = if coverage {
+    let deno_inspector = match worker.inspector.as_ref() {
+      Some(inspector) => inspector,
+      None => {
+        return Err(
+          OpError::other("coverage option requires --inspect flag".to_string())
+            .into(),
+        )
+      }
+    };
+    let inspector_url = Url::parse(&deno_inspector.debugger_url)?;
+    Some(CoverageCollector::connect(inspector_url).await?)
+  } else {
+    None
+  };
+
   let execute_result = worker.execute_module(&main_module).await;
   execute_result?;
   worker.execute("window.dispatchEvent(new Event('load'))")?;
   (&mut *worker).await?;
-  worker.execute("window.dispatchEvent(new Event('unload'))")
+  worker.execute("window.dispatchEvent(new Event('unload'))")?;
+
+  // TODO(bartlomieju):
+  // * stop collecting collecting coverage
+  // * wait for inspector client thread to join and return
+  // coverage JSON struct
+  // * parse coverage report to CoverageParser together with list
+  // of test files and prepare a test/JSON report
+  // coverage_collector.stop_collecting();
+
+  if let Some(coverage_collector) = maybe_coverage_collector.as_mut() {
+    coverage_collector.stop_collecting().await?;
+    eprintln!("stop collecting");
+    (&mut *worker).await?;
+    (&mut *worker).await?;
+    (&mut *worker).await?;
+    (&mut *worker).await?;
+    eprintln!("polled worker");
+    let coverage_report = coverage_collector.get_report().await?;
+    let test_modules = test_modules
+      .into_iter()
+      .map(|u| u.to_string())
+      .collect::<Vec<String>>();
+    let filtered_report = coverage_report
+      .into_iter()
+      .filter(|e| test_modules.contains(&e.url))
+      .collect::<Vec<CoverageResult>>();
+    eprintln!("test modules {:#?}", test_modules);
+    eprintln!("coverage report: {:#?}", filtered_report);
+  }
+
+  Ok(())
 }
 
 pub fn main() {
@@ -584,9 +645,9 @@ pub fn main() {
       include,
       allow_none,
       filter,
-    } => {
-      test_command(flags, include, fail_fast, allow_none, filter).boxed_local()
-    }
+      coverage,
+    } => test_command(flags, include, fail_fast, allow_none, filter, coverage)
+      .boxed_local(),
     DenoSubcommand::Completions { buf } => {
       if let Err(e) = write_to_stdout_ignore_sigpipe(&buf) {
         eprintln!("{}", e);
diff --git a/cli/tests/inspector_coverage.js b/cli/tests/inspector_coverage.js
new file mode 100644
index 00000000000000..3db0e5a19b6788
--- /dev/null
+++ b/cli/tests/inspector_coverage.js
@@ -0,0 +1,16 @@
+function a() {
+  console.log("hello a");
+}
+
+function b() {
+  console.log("hello b");
+}
+
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+function c() {
+  console.log("hello c");
+}
+
+a();
+b();
+b();