diff --git a/.gitea/workflows/testing.yaml b/.gitea/workflows/testing.yaml
new file mode 100644
index 0000000..1bbae74
--- /dev/null
+++ b/.gitea/workflows/testing.yaml
@@ -0,0 +1,37 @@
+# name of the workflow.
+# this is optional.
+name: Test Gitea Actions
+
+# events that will trigger this workflow.
+# here, we only have "pull_request", so the workflow will run
+# whenever we create a pull request.
+# other examples: [push] and [pull_request, push]
+on: [push]
+
+
+# each workflow must have at least one job.
+# jobs run in parallel by default (we can change that).
+# each job groups together a series of steps to accomplish a purpose.
+jobs:
+  # name of the job
+  first:
+    # the platform or OS that the workflow will run on.
+    runs-on: ubuntu-latest
+
+    # series of steps to finish the job.
+    steps:
+      # name of the step.
+      # steps run sequentially.
+      # this is optionale
+      - name: checkout
+        # each step can either have "uses" or "run".
+        # "uses" run an action written somewhere other than this workflow .
+        # usually from the community.
+        # this action checks out the repo code to the runner (instance)
+        # running the action
+        uses: actions/checkout@v3
+
+      # another step.
+      # this step runs a bash (Ubuntu's default shell) command
+      - name: list files
+        run: ls
\ No newline at end of file
diff --git a/.obsidian/workspace.json b/.obsidian/workspace.json
index 7abc687..636b8b0 100644
--- a/.obsidian/workspace.json
+++ b/.obsidian/workspace.json
@@ -24,6 +24,20 @@
           {
             "id": "53b36d00b704136e",
             "type": "leaf",
+            "state": {
+              "type": "markdown",
+              "state": {
+                "file": "Tests.md",
+                "mode": "source",
+                "source": false
+              },
+              "icon": "lucide-file",
+              "title": "Tests"
+            }
+          },
+          {
+            "id": "ec34d2df2728a299",
+            "type": "leaf",
             "state": {
               "type": "markdown",
               "state": {
@@ -36,7 +50,7 @@
             }
           }
         ],
-        "currentTab": 1
+        "currentTab": 2
       }
     ],
     "direction": "vertical"
@@ -179,13 +193,14 @@
       "command-palette:Open command palette": false
     }
   },
-  "active": "53b36d00b704136e",
+  "active": "ec34d2df2728a299",
   "lastOpenFiles": [
+    "Writing_Tests.md",
+    "Tests.md",
+    "minigrep/README.md",
     "minigrep/src/lib.rs",
     "Test_Organization.md",
     "Test Controls.md",
-    "Tests.md",
-    "Writing_Tests.md",
     "Traits.md",
     "Modules and Use.md",
     "Modules.md",
diff --git a/minigrep/README.md b/minigrep/README.md
index 9e6f48c..3a86dfb 100644
--- a/minigrep/README.md
+++ b/minigrep/README.md
@@ -727,4 +727,301 @@ We add `use minigrep::Config` line to bring the `Coinfig` type from the library
 
 And we prefix the `run` function with our crate name so that it can also be used
 
-This work sets up for success in the future.
\ No newline at end of file
+This work sets up for success in the future.
+
+### Sixth Goal: Developing the Library's Functionality with Test-Driven Development
+Now that the code and logic has been extracted out of *main.rs* and left behind the argument collecting and error handling
+
+It is now much easier and possible to write tests for the core functionality of the code.
+
+We can now call functions directly with various arguments and check the return values without having to call our binary from the command line.
+
+This goal's section will focus on adding the search logic to the `minigrep` program using the test-driven development (TDD) process with the steps:
+1. Write a test that fails and run it to make sure it fails for the reason you expect
+2. Write or modify just enough code to make the new test pass
+3. Refactor the code you just added or changed and make sure the tests continue to pass
+4. Repeat form step 1
+
+Even though this is one of many was to write software, TDD can help drive code design
+
+Writing the tests before you write code that makes the test pass helps to maintain high test coverage throughout the process.
+
+We will test drive the implementation of the functionality that will actually do the searching for the query string in the file contents and produce a list of lines that match the query
+
+We will add this in the function called `search`
+
+#### Writing a Failing Test
+First lets remove the `println!` statements because we don't need them anymore to check the program's behavior.
+
+Next we'll add a `tests` module with a test function the same as [The Test Anatomy](../Writing_Tests.md) from before.
+
+This test will specify the behavior we want the `search` function to have
+- It will take a query and the test to search
+- it will return only the lines form the text that contain the query
+Here is the test (it goes in *src/lib.rs*)
+Note it will not compile yet
+```rust
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn one_result() {
+        let query = "duct";
+        let contents = "\
+Rust:
+safe, fast, productive.
+Pick three.";
+
+        assert_eq!(vec!["safe, fast, productive."], search(query, contents));
+    }
+}
+```
+This test will search for the string `"duct"`
+
+The test we will search three lines only one that contains `"duct"`
+
+Note that the backslash after the opening double quote tells Rust not to put a newline character at the beginning of the contents of this string literal.
+
+We will then assert that the value returned from the `search` function only contains the line we expect
+
+We aren't yet able o run this test and watch it fail because the function it needs in order to compile and run doesn't exist yet.
+
+In accordance with TDD principles we will add just enough code to compile and run by adding a definition of the `search` function that always returns an empty vector that doesn't match with the one in the assert.
+
+Here the what the function will look like at this point
+```rust
+pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
+    vec![]
+}
+```
+
+Notice that we need to define an explicit lifetime `'a` in the signature of `search` and use that lifetime with the `contents` argument and the return value.
+
+This case specifies that the vector returned should contain string slices that reference slices of the argument `contents` (rather than the argument `query`).
+
+It also could be said that the returned value will live as long as what was passed into the `contents` arguments.
+
+This is important the data referenced *by* a slice needs to be valid for the reference to be valid.
+
+If the compiler assumes we are making string slices of `query` rather than `contents` it will do its safety checking incorrectly.
+
+
+If we forget lifetime annotations and try to compile we will get this error
+```
+$ cargo build
+   Compiling minigrep v0.1.0 (file:///projects/minigrep)
+error[E0106]: missing lifetime specifier
+  --> src/lib.rs:28:51
+   |
+28 | pub fn search(query: &str, contents: &str) -> Vec<&str> {
+   |                      ----            ----         ^ expected named lifetime parameter
+   |
+   = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `query` or `contents`
+help: consider introducing a named lifetime parameter
+   |
+28 | pub fn search<'a>(query: &'a str, contents: &'a str) -> Vec<&'a str> {
+   |              ++++         ++                 ++              ++
+
+For more information about this error, try `rustc --explain E0106`.
+error: could not compile `minigrep` (lib) due to 1 previous error
+```
+
+Rust can't possibly know which of the two args we need so we need to tell it explicitly.
+
+Due to `contents` is the arguments that contains all of our text we want to return the parts of that text that match.
+
+This shows that `contents` is the argument that should be connected to the return value using the lifetime syntax.
+
+Other programming languages don't require you to connect the arguments to return value, but this practice will get easier over time with more exposure.
+
+Here is the output of the test
+```
+$ cargo test
+   Compiling minigrep v0.1.0 (file:///projects/minigrep)
+    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.97s
+     Running unittests src/lib.rs (target/debug/deps/minigrep-9cd200e5fac0fc94)
+
+running 1 test
+test tests::one_result ... FAILED
+
+failures:
+
+---- tests::one_result stdout ----
+thread 'tests::one_result' panicked at src/lib.rs:44:9:
+assertion `left == right` failed
+  left: ["safe, fast, productive."]
+ right: []
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+
+
+failures:
+    tests::one_result
+
+test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
+
+error: test failed, to rerun pass `--lib`
+```
+This test fails exactly as expected
+
+#### Writing Code to Pass the Test
+Our test is failing because we always return an empty vector
+
+To fix this and implement `search`, the program needs to follow these steps:
+1. Iterate through each line of the contents
+2. Check whether the line contains the query string
+3. If it does add it to the list of values we are returning
+4. If it doesn't do nothing
+5. Return the list of result that match
+
+##### Iterating Through Lines with the lines Method
+Rust includes a helpful method to handle line-by-line iterations of strings, named `lines`
+
+Here it is how it would be used in this case
+```rust
+pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
+    for line in contents.lines() {
+        // do something with line
+    }
+}
+```
+The `lines` method returns an iterator.
+For now recall that when used in a `for` loop with an iterator to run some code on each item in a collection
+
+##### Searching each Line for the Query
+Next we will check whether the current line contains our query string.
+
+Strings have a helpful method named `contains` that does this for us.
+
+now lets add a call to the `contains` method in the `search` function
+
+Here is the updated function
+
+Note it still will not compile
+```rust
+pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
+    for line in contents.lines() {
+        if line.contains(query) {
+            // do something with line
+        }
+    }
+}
+```
+At the moment we are only building up functionality
+
+To get the code to compile we need to return a value from the body as we indicated in the function signature
+
+##### Storing Matching Lines
+To finish this function we need a way to store the matching lines that we want to return.
+
+To do this for now we can make a mutable vector before the `for` loop and call the `push` method to store a `line` in the vector
+
+After the `for` loop the vector will be returned
+
+Here is what the function like after adding the `vector` and the `push` method
+
+Note it will now compile
+```rust
+pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
+    let mut results = Vec::new();
+
+    for line in contents.lines() {
+        if line.contains(query) {
+            results.push(line);
+        }
+    }
+
+    results
+}
+```
+Now the `search` function should return only the lines that contain `query` and the test should pass
+
+Here is the output when running the test at this point
+```
+$ cargo test
+   Compiling minigrep v0.1.0 (file:///projects/minigrep)
+    Finished `test` profile [unoptimized + debuginfo] target(s) in 1.22s
+     Running unittests src/lib.rs (target/debug/deps/minigrep-9cd200e5fac0fc94)
+
+running 1 test
+test tests::one_result ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
+
+     Running unittests src/main.rs (target/debug/deps/minigrep-9cd200e5fac0fc94)
+
+running 0 tests
+
+test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
+
+   Doc-tests minigrep
+
+running 0 tests
+
+test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
+```
+
+As we can now see the test passes.
+
+At this point we could consider opportunities for refactoring the implementation of the search function while keeping the tests passing to maintain the same functionality
+
+The code in the search function isn't too bad but it doesn't take  advantage of some useful features that iterators have
+
+This will be further improved in the iterators chapter
+
+##### Using the Search Function in the `run` Function
+Now that the `search` function is working and tested, we now need to call `search` from our `run` function.
+
+We need to pass the `config.query` value and the `contents` that `run` reads from the file to search function.
+
+Then `run` will print each line returned from `search`
+
+Here is what run will look like now
+```rust
+pub fn run(config: Config) -> Result<(), Box<dyn Error>> {
+    let contents = fs::read_to_string(config.file_path)?;
+
+    for line in search(&config.query, &contents) {
+        println!("{line}");
+    }
+
+    Ok(())
+}
+```
+
+We are still using a `for` loop to return each line form `search` and print it
+
+Now that the entire program should work
+
+Lets try it with first with a word that should return exactly one line from the Emily Dickinson poem: *frog*
+
+Here is the output
+```
+$ cargo run -- frog poem.txt
+   Compiling minigrep v0.1.0 (file:///projects/minigrep)
+    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.38s
+     Running `target/debug/minigrep frog poem.txt`
+How public, like a frog
+```
+
+Now lets try with a word that will match multiple lines like *body*
+```
+$ cargo run -- body poem.txt
+   Compiling minigrep v0.1.0 (file:///projects/minigrep)
+    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s
+     Running `target/debug/minigrep body poem.txt`
+I'm nobody! Who are you?
+Are you nobody, too?
+How dreary to be somebody!
+```
+
+Then lets make sure we don' get any lines when we search for a word that isn't anywhere such as *monomorphization*
+```
+$ cargo run -- monomorphization poem.txt
+   Compiling minigrep v0.1.0 (file:///projects/minigrep)
+    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s
+     Running `target/debug/minigrep monomorphization poem.txt`
+```
+
+Now that it is finished we will finished off with a demonstration on how to work with environment variables and how to print a std error, both are useful when you are writing command line programs
+
diff --git a/minigrep/src/lib.rs b/minigrep/src/lib.rs
index 488b891..7f95b91 100644
--- a/minigrep/src/lib.rs
+++ b/minigrep/src/lib.rs
@@ -23,7 +23,39 @@ impl Config {
 pub fn run(config: Config) -> Result<(), Box<dyn Error>> {
     let contents = fs::read_to_string(config.file_path)?;
 
-    println!("With text:\n{contents}")
+    // refactor 10
+    // println!("With text:\n{contents}")
+
+    for line in search(&config.query, &contents) {
+        println!("{line}");
+    }
 
     Ok(())
-}
\ No newline at end of file
+}
+
+pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> {
+    // original that only can fail
+    // vec![]
+
+    for line in contents.lines() {
+        if line.contains(query) {
+            // do something with line
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn one_result() {
+        let query = "duct";
+        let contents = "\
+Rust:
+safe, fast, productive.
+Pick three.";
+
+        assert_eq!(vec!["safe, fast, productive."], search(query, contents));
+    }
+}
diff --git a/minigrep/src/main.rs b/minigrep/src/main.rs
index ed6a23e..0049ff4 100644
--- a/minigrep/src/main.rs
+++ b/minigrep/src/main.rs
@@ -30,12 +30,13 @@ fn main() {
     //     process::exit(1);
     // });
 
-
-    println!("Searching for {}", config.query);
-    println!("In the file {}", config.file_path);
+    // refactor 10
+    // println!("Searching for {}", config.query);
+    // println!("In the file {}", config.file_path);
 
     // refactor 8
     if let Err(e) = minigrep::run(config) {
+        // needed for helping the user
         println!("Application error: {e}");
         process::exit(1);
     }